Asphalt is soft, and will become very soft in the heat. Let's say you plan to park an RV or store a boat on it for long periods of time in the summer, the wheels can literally sink into the surface of the asphalt. Concrete pads simply support huge loads without deforming.

Why not just go through the wall? Permanent installation while you use it and easy to patch if you don't want it anymore?

Can't see the pix, but you can run a 2-wire 14-gauge from the new outlet to the switch and just screw in the black wire to the load side of the switch - you can have two wires on a switch load. Some switches have the ability to receive a wire pushed in on the backside, sometimes you have to run a short wire from the switch nut to and bind 3 wires together - up to you.

Water running down the wall is the issue for older windows. Rain is not the main issue because any water, including from a garden hose or high pressure sprayer, can cause water to run down the wall of your house.

You'll notice the window has a similar ledge on the bottom of it to divert water running down the window away from the bottom edge of the window in order to prevent water from seeping in under the window into the wall. Similarly, this ledge above the window is intended to divert water away from the top edge of the window so it doesn't run down the wall and seep into the wall above the window. These design features are common in older windows that were installed flush with the exterior of the house. In even older buildings, windows were recessed in thicker walls which eliminated the need for these ledges, as long as the lower part of the wall was canted to drain properly.

This water seeping in around windows has historically been a major issue of failure in buildings and was solved in modern construction windows by including a flange as part of the window frame, so any water seeping down the walls is stopped at the flange. It works so well, no one builds these drip ledges anymore.

Your installation is considered "hard wired" and you do not need a junction box as long as you wire the dishwasher directly into the electric line.

The last kitchen remodel I did, the owner didn't know if they wanted a dishwasher yet because the kitchen was so small, but they wanted power available in case they changed their minds in the future. In this case, I terminated the circuit in a junction box under the sink cabinet which was next to the cabinet that would have been removed to install a dishwasher.

As long as a dishwasher is a permanent part of your kitchen, you don't need to install a junction box and hard wiring as in your current configuration is the best choice and meets code.

What is not acceptable is terminating a circuit in a hidden junction box, like behind the dishwasher, because all junction boxes are required to be accessible to look for evidence of arcing during an inspection. In the case of a direct or hard wired dishwasher, the junction box is actually installed beneath the dishwasher where the electrical connection is made and is considered to be a safe way to wire an appliance.