1) One thing you could do when contemplating adding a new type of magic system is running a 1-shot adventure that revolves around the new rules. If you like it, add it. If you fear the time constraints, you could design the RPG equivalent of a training/obstacle course and just run parties through it, evaluating the classes- how does the PsyWar handle in the same fight as you'd expect a Barbarian to handle? How does he compare to the Paladin? How good is a Shadowcaster in "wizardy" fire support as opposed to a Psion?
2) Good Psionic PC concepts? That's subjective. However, typical builds you'll find are:
a) Psions as blasters, and Wilders as Sorcerer analogues. They're gooooood at it. Downside- if they burn too brightly, they'll burn most quickly. Like other base casters, there are a number of PrCls tailored to them- the Mystic Theurge has a Psionic/Arcane version and a Psionic/Incarnum variants, for instance.
b) PsyWars as Expanding head-crushers. Expand is Psionics' equivalent to Enlarge, but can boost a PC 2 steps in size. Coupled with a 2 handed weapon or a reach weapon, he's dishing out LOTS of damage. Add a race with powerful build (XPH's Half-Giants or Races of Stone's Goliaths) and there is a further bump. Of course, they also work well with the Kensai PrCl.
c) Soulknives as Wizard-hunters/Assassins. Armed with a weapon that is nearly impossible to get rid of that ultimately can do damage to the 3 caster stats, they do that job nicely. (Some call them underpowered...but that's usually because people compare them to Fighters, when they should be compared to classes like the Monk. Besides, a lot of that gets rectified with Dragon #341, Hyperconscious, and CompPsi.)
d) Don't like the Psionic Base classes? PCs with the Wild Talent Feat or members of races that are naturally psionic can qualify for certain psionic PrCls (like the Pyrokinetic and the WotC website variants for
other energy types, for example) while otherwise sticking to Core classes. A githzerai monk is pretty archetypal...but add in levels of the Electrokinetic PrCl and you've got Raiden from Mortal Kombat. A Xeph Bard with levels in Sonokinetic could sing his opponents to death- contributing directly where most Bards merely buff. A Thri-Kreen Barbarian/Acetokinetic would rage into battle coated in his acidic nimbus, slashing wildly with his natural weapons... And, of course, a naturally psionic PC (or one with Wild Talent) qualifies for all those nice Psionic feats.
But this is just stuff anyone could come up with- ask your players what they would play if they could play psionic PCs. They might surprise you.