2.5e bandits have a unique stats? news to me. While I'm assuming the 1e version of TOEE, I'll see if I have a copy of a later 2e reprint to see if anything much was changed (which I doubt, TSR was very lazy on such things, which actually were work pre computers)
L0 bandits, brigands, soldiers, mercs, pirates, buccaneers, etc will all convert to warriors (optionally, some could be commoners or experts, but there is little point making things hard on yourself, keep them homogenized for ease of use)
Other L0 NPC's should be easy to determine; commoners mostly, with experts for more skilled craftsmen & professions.
Rhennee are well described in the 1e world of greyhawk boxed set. They are akin to water based gypsies. For 0L types, probably the expert class. I don't recall them being too prevalent in TOEE
Now, it is entirely possible, even desirable to give levels beyond 1 to these former L0 type. It depends on your method & style of conversion for the adventure(s). Moreover, you will find bandits & such with levels or HD among the rest...these would have been fighters in 1e (& often will be listed as such). You can convert them as fighters, or else make them warriors as well, but in the later case I recommend raising their level (HD) by AT LEAST 1.
Feats for L1 warriors/bandits? Again, I'd keep it simple, and frankly, despite what was said earlier by others, 1e or 2e style stat lines are a better way to go! Anyway, toughness, WF, improved init, lightning reflexes, point blank shot, precise shot, alertness, stealthy, able learner, etc. Pretty basic stuff, with perhaps something of use from post PH (such as able learner)
Skills? intimidate, spot, listen, move silently, hide, survival for bandits. Other than the first, all cross class for warriors.
Some examples.
TOOE pg 50 (read descriptions, etc) has guards with stat blocks of "Guards (5): AC 4, MV 9", Level 0, hp 7, 6, 5, 5, 5, #AT 1, D 1-8 (longsword) or 2-5 (crossbow bolt); SA javelins (D 1-6, ranges 2 "/4"/6"); XP 21, 20, 19 (x3)"
a direct conversion could be:
"earth temple guards" human warrior L1 AC 16 (mail, light shield) SPD 20 HP: 5 ea, init +4 BAB+1, F +2 R+0 W+0, long sword (+2 d8+1), 2 have heavy crossbows (+1 d10 120'; no shield use to start), 3 have javelins (+1 d6 30') S: spot+4, listen+4, sense motive +2 F: improved initiative, alertness S 12 D 11 C 10 I 10 W 11 CH 9
it is enough for the DM to know they have touch AC 10, etc
The way d20 works vs AD&D though, direct conversions may well let you down.