Alright, I'm going to preface my advice: I play on the Kong server, which is innately different from AG/FB, primarily through being devoid of the DMU, which ****s with the ingame economy (uni inflation). That being said, I have heard of crazy prices being paid on AG/FB that are unheard of at Kong.
Notes, Infamous ones aren't very hot on trade, but research ones are, ones most in demand are production, storage, and equipment. Lucky unis, they have been found to be a mixed bag of stats (non-lucky have better base stats, lucky ones compromise some of that for item chance), so I wouldn't trust them having much value. Skilled unis are OP, command a high MP, I would sell those, or use them yourself.
For PvE, you need bandos, bandos in the 70-80% range are cheap yet practical, all your gunners (recons, fighters, leader, etc.) gets one to boost their weapon dps.
Scavengers, medic, they can get the
That will get you done with the basics you need to function. Any extra, spend on the best SCAR you can afford (aps comes first, extra capacity is nice).