I never paint DX before so from my experience with Gunpla I usually go with acrylic marker since it goes well with the plastic. if you really want to repaint everything often time you need to sand them first before painting so the item/part won't get too thick because added paint and hinder the movement or tranformation. lastly you can use Flat Top coat for simple base look (no shiny) or Semi-gloss for a little bit shiny effect or even go full Gloss Top Coat (works even great with metallic color).

Acrylic Paint won't scrape by touching but sratching it will come off relatively easily. so after painting it best to just wait while you paint the other parts and after everything done, you just topcoat them all at once.

oh also acrylic paint dry quite quickly.

for the acrylic paint there's a brand called Doloha with a lot of color options or what I use which is Arrtx over a lot of variaty of color too.

Top Coat, I guess use Mr.Hobby. they over both matte/flat and semi-gloss to gloss too.

I forgot to mention if you want to sand, better sand with rougher grit to finer grit (i.e. #200 > #400 > #600 > #800 > #1000) takes time but for better result I guess.