Tank size really 3 foot but i guess you could go a little smaller
Like most plecs very peaceful, may get a little aggressive over food but many fish do this
PH isn't a major issue (they will adapt quite well) as long as it's not a major difference to what they were originally kept in and the Ph isn't extremely high but good acclimatizing should always be done anyways.
They arnt a huge plec so around 6 inches is probably max but could get slightly bigger, could get slightly smaller
They need wood in the tank as it's a panaque species and requires wood for it's diet, good varied diet of veg should be offered along with the occasional meat/protein source.
Other than that a nice plec and a nice addition to most tanks