> Back prime and paint the

Back prime is a very short way to say "prime and pain the back side of anything you put up", I was specifically talking about priming and painting the back side trim itself in that case. You would also generally want to put at least one coat of paint on the front after installation to cover up the installation marks. I'd usually prime the whole wall and the front & back of the trim, give just the corner of the building and the backside/edges/end of the trim a coat of paint then re-prime the front of the trim after installation then paint over the whole thing. This is possibly overkill but it gets all of the surfaces nicely coated and is something resembling best practices.

For drainage and moisture prevention on the base you basically have two problems you're trying to solve.

First is to ensure that running water from like rain and snow melt will drain around the building and not into the building. So if the dirt up slope has slumped in along the foundation you'd want to dig it back a smidge and ideally grade it out to an even slope so it's less likely to slide in quickly. If it's loose dirt it's also probably a good idea to put something like some landscape fabric and bark chips or sod down to keep initial erosion from happening. This also means you should eyeball the overall drainage on the upslope side to ensure that there aren't any dams that water can get trapped behind. If the dirt isn't built up to where it'll block drainage and is stable then generally try to avoid disturbing it to much as that will likely increase future erosion (so it's kind of a trade off.. if there's a problem.. fix it.. but if there isn't then don't.. heh). Naturally compacted soil is usually fairly stable (moreso than most homeowner "compacted" anyway).

The second problem is vegetation and debris that can built up on top of the soil. This can/will wick moisture up and hold it in contact with the building and prevent it from drying out which will cause rot. This is often a problem around buildings where folks don't dig the down the dirt enough

One thing to remember about moisture is that it needs to be able to move. Ideally it moves to the outside of and away from the building. If you look at "good" (from an engineering perspective aesthetics are a separate problem heh) construction you'll start seeing this in all phases of the design from site prep to building shell design to window install to how exterior trim is designed and applied.

If you want some really interesting (interesting is I suppose relative.. heh) reading on building design https://buildingscience.com/ has a bunch of really fascinating articles and papers on building design and how they can go well or wrong. You can search for basic concepts there with google like "site:buildingscience.com back prime trim" (minus the quotes obvs).

Example relevant to the trim question: https://buildingscience.com/documents/building-science-insights-newsletters/bsi-015-stress-relief

I think the big question isn't answerable from the picture and that's whether the frame and foundation is still good. OP when you get there take your pocketknife or a screwdriver and go around the inside of the base of the shed and kind of poke at things every few inches. If it's solid then that's good.. if you can poke into it easily that's bad. If it's just soft in a couple of places you can often fix that by bracing up that side and cutting out the rotten bits and sliding in new pressure treated. OTOH if it's rotten all around most of the base it starts getting a lot easier to just tear down and rebuild. You can also do the same poke-for-rot around the accessible bits of the outside.

There is a similar concern if the roof has been leaking that some of the roofing timber or sheathing might be rotten but that lands more firmly in the fix territory IMHO.

If I had to bed.. I'd bet on fix in this case. Although there's some clear rot on the threshold which makes me wonder a bit. And I'm mildly concerned about the sill plate on the uphill side where all the trash is.

It looks like there's a concrete foundation. You might do well to pull back some of the trash (those pipes and shit are collecting leaves and holding moisture there) and maybe a touch of the dirt from the uphill side of the shed to make sure water is draining around it and not into it. You basically want to make sure the bottom of the wood is not touching anything except the concrete. No leaves, no dirt, no trash.. and there's a couple inches of drainage below the wood as well.

I don't think I'd get overly fancy with the door, it's been patched at least twice.. pull that off and put some 1/2" treated plywood on it and good to go. That's assuming it's not in worse shape than I can tell which.. is about 50/50 odds from here hah. If you do need a new door if there's a local rebuildit or habitat for humanity or similar store around you that's a good place to get them for not to much.

Be somewhat careful with the tin overlay someone was suggesting. The idea with outside covering is you want the water to always have drip out. So you basically want all layers to look like

inside \\\\ outside

so they drain to the outside and there's no place to trap water. Simply slapping a sheet of tin around the bottom is a place to trap moisture behind and will likely cause the wood behind it to rot faster. If you cut the siding back and slid the tin up under it that could work.. but I doubt it's worth the effort.

If any of those limbs look like they can smack the roof/side of the shed in a breeze trim them back so they can't.

Use a push broom to gently pull the needles back off of the roof. If the roof it leaking but not to badly you can patch it with some roofing tar. If the decking (plywood under the shingles) is rotted out you'd have to replace the roof. If the rafters are rotten you can cut new ones to match and "sister" them alongside the existing when the roof decking is off. Putting on a new rood isn't terribly hard.. but would take a newbie soloing probably a couple days just to figure it all out.

You might have to replace some/part/all of the door frame. Looks like it's probably just 1x4's. If so you'll see how they're nailed on when you pull them off.. do the same. Back prime and paint the wall and the back sides of the replacement boards before you put the new ones up. If they ain't rotten don't replace them.. but they look kinda rotten.. You can also use some 1x4's or 1x3's to replace trim the corners that should cover that gap in the upper left side as well :) They're basically just nail one flush to the building corner and then nail the other one to it overlapping and also to the wall. Pay attention to how the ones are on there now and you'll figure it out.

You'll minimally want a hand saw, a claw hammer, a cats paw tool, a flat pry bar, a framing square (speed square is nice but not strictly necessary but for $10 extra...), a level, some 10 penny galvanized nails, and some 2" galvanized box might be useful for the edges of the trim, if you get into the door you'll also need a screw driver for the hinges (drill/driver would be my recommendation) and some shims for resetting the door frame. If you have to do the roof add a circular saw for cutting the plywood roof decking to size, a chalk line for marking the plywood and the roof tile lines, a roofing stapler for laying the felt, some roofing nails, enough felt to cover, drip edge, replacement wood where needed, box of roofing nails, probably 2 maybe 2.5-3 squares of shingles and a stack each of starter and ridge shingles.

Basalt rebar is taking up some of that role, higher tensile strength, less corrosion. Cost is still somewhat high though.

some of the old L shaped iron rails on wooden tracks that were used well into the 1800's in mines (because they're light..) wouldn't be that hard to reproduce for a straight run.. Combined with an electric winch set on a deadman at the top (inside a covered cart stop..) and you'd have a pretty cool system.