I agree with everyone buying a 5th Hood Blue would help you out long term, PVP and PVE. You don’t need to level him, because at 5 Blue, he doesn’t steal more or less based on level. I am not sure you would want to use HP to buy Mystique covers, because I don’t think she is someone that would that could be a mainstay in your PVP roster. Since the goal is usually do well in PVE until you can do well in PVP, you should be thinking of leveling people that will help you out in the long term. It might be too early for you to pick anyone to level, because you never know how the covers will fall. If you are willing to buy 2 Green and 3 Black for xforce, it will make your 3* transition a lot easier, because you’ll be able to win more covers in PVP. Covers and the 3* dilution are what initially stalls your transition process. It becomes ISO at a point, when you don’t have the ISO to level the characters you have optimally covered.
Buy a blue cover for Hood and give him a few levels. Then either buy covers for XF Wolvie (two green = 5000 HP, ouch) or start leveling Mystique. Mystique has low health but is otherwise quite good. Her blue at 5 covers is really good, and I think it would work well with OBW.
I would not bother with Storm without 4* Thor or maybe Star-Lord. Captain Marvel can be fun alongside a powerful 2* red user, but long-term she’s not so hot.
I would also disagree with this. Unless you’re prepared to drop the HP to max out Surgical strike or X-Force Green (which is going to be costly), a 3/2/3 X-Force at level 168 is going to be a really juicy target in PvP, and will also mess up your PvE scaling. I’d add my voice to the advice to level Mystique, and combo with MagsMN, especially as her softcap is about right to mesh with your existing 2*s. I’d also agree with the fifth blue cover for Hood. Otherwise, if you’re not in a rush, I’d take my time, and wait for a few more covers to drop.
So I went ahead and dumped all my ISO into MNMags (he was lvl 29 yesterday, now maxed at 94) and Mystique (currently lvl 96 I think), and damn is this a great combo. Magneto’s purple feeding Mystique’s blue which then feeds Mag’s purple again…so OP. With a good board and a little luck and planning I have had some games be over after my first 3 purple matches - enemy never gets another turn - and that is without even using any boosts.
I got my 10-pack from this season this morning and what was in there? Why 
of course!!! 
So once I get some HP I’m thinking definitely blue hood, and 2x green XF, probably that last blue Mystique, and maybe the last two black hulk covers. That would be what 10,000 HP? Would give me a pretty solid PvE and PvP offense, with a PvP defense that probably won’t scare too many off, but just might get me some wins with fully covered Anger + XF. And I’ll have another 10k+ HP to drop into XF’s black and whatever else comes my way later on down the road.
Its likely just personal preference but Im not sure I would spend on Hulk, he hasnt come off my bench in a LONG time. For advancement I would still advocate for cover maxing XF at 5/5/3, then Hoods blue (so 5/5/1) for a cost of 13750HP.
Even under leveled XF/Hood is so much better than just about any Hulk+??? team (aside from the semi-suicidal Patch/Hulk). I love seeing maxed Hulks as I know Ill take some damage (I go a few extra match turns before 1-turn wiping hulk, so whatever 3 or 4x match damage is) but its generally an easy match. Part of that is that if Hulk is center, or left and higher than featured XF SS will then grab green, clear out the opps green, do a hefty chunk of damage (at 220 Ive done 6k+ SS damage which would have chained into TWO XF, if the char had survived), and rid the board of green such that Anger cant do much.
My favorite duo is XF and CMa, who isnt worth spending on til you get a few more covers, and add in Hood if you get three. I typically ride this to T25, or T10 if I shield at least once. I just rode it to 2,400 in SHIELD yesterday too, no shielding. Highly efficient, and if you are willing to drop 2x G/Blk boost it is just about unstoppable.
Just wading in but one bit of advice I didn’t see in initial scan is once you choose who you are going with in your transition (maybe 3-5 characters), level everyone evenly when possible especially if PVE is your preferred format. Don’t let Hulk and XF get too out of balance, level wise, from the rest of your team. The game really punishes you for high variability in your character levels. It doesn’t look like an issue yet but if you race to 166 with Hulk and don’t have 2-3 other guys that are right there with him, it is going to play with your scaling in PVE for the worse.
I subscribe to the 135 for all except XF way of leveling. No one goes above it and XF is 145. Still get my challenges in PVE but I’ve never seen 395 max nodes like some vets. Usually in the low 200’s is my worst case. Why take more time on a node if I don’t have to? I can also take on most PVP through the 700’s when I need to but I don’t focus on it and go unshielded many events.