Gotcha. Just wanted to know what we have to work with. So, here are some turtles I have kept with T. scripta and had no problems with:
Sternotherus minor peltifer
S. odoratus
Chrysemys picta
Pseudemys concinna
Graptemys geographica
G. ouachitensis
I suspect any aquatic emydid would do fine, as would any kinosternid. Softshells and of course snappers should be avoided. I have no experience with Fly River turtles, batagurids, or side-necks, so I won't comment on them.
A possible issue is the difference in feeding aggression; passive turtles like painteds may be overwhelmed by more aggressive sliders and not get their share. I throw food to several places in the tank to prevent the turtles from being in direct competition. You may see a little nipping as well, when new turtles are added or at feeding time. This is usually harmless, but keep an eye out for turtles that routinely are intimidated as they may become stressed or injured.
Your current setup sounds good, you've obviously done your research. I'd add some plant matter to the turtle's diet. Dark lettuces (not iceberg), collards, kale, anacharis, duckweed, and slices of various fruit or vegetables are all good; he may not go for them at first, but should eventually try them. Chrysemys and Pseudemys species are more vegetarian than sliders, so if you get some of those this goes double.