In case of armor plates T2P is in fact very much the way to go, the weight savings are enormous and the build cost are quite reasonable, even for use in PVP. Profit can be made there no doubt!
Because T2P is a fitting and weight optimization of T1, you should focus on those modules that are used in PVP and weight a lot in T1. For PVE fitting and increased performance is the area to look into. Everything that people use on their logistic bots, tuners and weapon systems is what work well.
In my own case, for PVE combat I use T3P machine guns in combination with T4P tunings. This saves a lot of ammo for the firearms platform at only a modest decrease in DPS, which is compensated for mostly by the tunings. Other weapon systems might fair similar in combining tiers, I would need to investigate that first...
Oh and if you found you sold all shield hardeners in Tellesis.....me bad, just had 3 accounts slip into heavy mech and glider haulers .