After claying will I need to polish with the 205 or WG FG? Or will the claying even harm the work I've already done?
There's been some chatter lately about how some people are seeing light scratching in their car's finish after claying and I would have to say that I've seen this too but luckily it's rare and in most cases will be more related to the paint being scratch sensitive, not because clay is evil.
I was working on a show car this year, black in color and noticed during clay demonstrations the paint was being scratched so I removed the scratches with a DA Polisher and a light polish.
It's one of the few times I've ever seen claying leaving scratches in the paint.
The goal is to use the right clay and a quality lubricant along with good technique whenever you're claying paint, but even so, inspect the results afterwards.
When it comes to removing overspray or any other "Above Surface Bonded Contaminant", at this point in time claying is the best alternative out of your choices because claying will remove above surface bonded contaminants without removing paint. You're other options without getting super complicated with some kind of chemical that will dissolve overspray but won't dissolve the car paint are some type of abrasive product like a compound, the problem with a compound however is that it's usually not as effective as claying at removing overspray depending upon how it's applied.
If applied with a foam pad any any kind of electric polisher including a rotary buffer the foam will merely glide over the bumps of overspray, some overspray will be removed but not all the overspray, that's why I use the word "effective" above.
If a wool pad is used on a rotary buffer to remove overspray then it's a lot more effective but now the fibers of the wool pad, the compound and the remove overspray will leave swirls in the paint and now you'll have to remove these.
So at this point in time, claying is the best choice or alternative for removing above surface bonded contaminants, just use GREAT quality products and GREAT technique, (you can use good products and good technique if you want to since it's your car but it sounds like you're going to want to do your best so I used the words great instead of good), and then inspect the results and move on from there.
Me personally? If I were in your shoes I would clay the paint to remove the overspray, the re-polish the paint to a crystal like shine and then re-seal the paint with a quality wax or paint sealant, especially if the car in question is important to me or my “toy”.
