Help With PvP Rankings

Unknown

I am on Day 440 in a row and I am finally making some progress in the transition to 3*. I have the following heroes that I use most frequently:

3*: 166 LT (3/5/5), 166 Pun (5/3/5), 145 GSBW (5/4/4), 140 BP (3/3/5)
2*: 94 Thor, 94 OBW, 94 CStorm, 94 Ares, 94 Wolvie
1*: 50 IM, 50 MStorm, 40 MBW (I keep these for the 1* events and DPD)

Other 3 stars in decent shape: 130 Sentry (5/4/4), 105 Patch (4/1/3), 105 Steve Rogers (3/3/5), Human Torch (3/3/5), Doom (4/5/1), Hood (3/3/1), CMag (4/5/0), Loki and Mystique (at least one of each cover)
4* (none really usable): IW 8 covers, XForce 6 covers, Dinosaur 4 covers, Nick Fury 2 covers, Star Lord 1 cover

Relying on LT, Pun, GSBW and BP I find I can get up to 450-500 in PvP without too much issue - once I get there I feel like I am done - everything I see is 200+ and looks very hard to beat. I also find that the longer I play the better the CPU's luck gets and I find a team of low 100's crushes my team- consistently - it is very frustrating. I don't mind spending a little money on covers but I'm not sure if/where I should spend it next. I have no reserves of ISO or HP. I don't mind grinding but once my 5 health packs are gone, I will not buy any. I think I have a decent team of 3* to work with. I will not spend money on gold tokens - I barely get golds on the ones I win while leveling in PvE and PvP.

Any tips for how to work my way up so that I can start getting up to 900 or so and earn the 4* covers? Are there better slices to get into? Does tanking still work? Any help to elevating my game would be most appreciated...