Generally you go 1/8" larger to make sure there is room for the epoxy all around. Check the size of the mounting holes on the posts. If they are half inch, you can increase the size of the threaded rod a bit - I would go up to 3/8" rod, and drill 1/2" holes (leaving 1/8" to fill with epoxy). You want a little "wiggle room" to get the spacing of the studs right and to fill all around with epoxy. Read the Hilti instructions - they are good - and there are some youtube videos. This is a very basic video, but shows the process (you don't need the extra step shown after using a core drill - that is something unusual) - the related videos below it are also good - https://www.youtube.com/watch?v=TsonKFh0UUw

If you are doing something that is fussy, transfer the pattern to some plywood, drill the same hole pattern in that, and hold the studs in place with two nuts (one on each side of the plywood) and make sure you can get that in and out of the drilled holes without binding up. You can even leave the plywood in place during the glue cure (just don't accidentally glue the nuts or the plywood to the concrete!).

You still have the same requirements to clean the dust out of the holes, using a small brush (I stole the brush that came with one of those reusable straws my kids had to have...) and some compressed air. Vacuuming can be part of it, but it won't get the dust out of the very bottom by itself. Sticking a thin tube down to the bottom and blowing it out with compressed air is better (but don't breath the concrete dust!).