You have Aegon, Doom/SS, Nick (better bring him to rank 5 before you go in) and maybe Heimdall as 4*. But you don't have either Void or HT, so you have to wait to get one of them to complete your Team for AOL, also void is better than HT for easy path and SS is better than Doom for easy path .
About how many Units you need, I will say 4k - 5k depend on how skilled you are and how many revives and heal potions you have in stash or planing to farm.
U can use sunspot or colossus for mephisto...other than that u have the 3 horsemen..as for the final slot u can keep hiemdal or mags(to help with the metal champs) I would recommend 5k units to be on the safer side and not worry about units towards the end of ur run
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Save 3-5k units
About how many Units you need, I will say 4k - 5k depend on how skilled you are and how many revives and heal potions you have in stash or planing to farm.
Your roster is missing torch/void and unit man from the typical team..
The rest you can do for 3-4k units, even if you are a scrub, with some hoarding/farming. Aegon, units and doom solve a lot of problems.
You can auto fight winter soldier with apoc, collosus and red mags really easily too, to farm lv3 potions, which really, really helps.
I would recommend 5k units to be on the safer side and not worry about units towards the end of ur run