I will help you out, don't do EP8(M3), do very easy mode and farm there, until you get a crystalline weap/hat, eternalized weap/hat. I got all my obsidians, elixir, Mythical hats(i literally got 3 mythicals in one map), insolences, crystal legends, eternals, nadrojis just skipping right to the cartographer from floor 200 to floor 400 on very easy mode(I used a battle mage item, and used charge to charge my way to the end of the map. Or do M3 floor 200 and farm there, but best thing to do is to go very easy mode till you climb to around 400/500 floor.
Right now my farming build cannot really handle M3 mode at 300+, but I am on floor 270ish M3 with my 80% finished farming build, and started again at floor 200 but this time at M3 mode, and I am having bits of trouble, but it is viable, and this time around i use hunter ring for the shrines to farm the feats.
But what's really important for you to understand is that you are not suppose to be able to farm M3 on those floors anyways with your build, best is to either do Epic Mode/M1 with less HP, or do very easy and climb/skip to Cartographer. (If you think about it, you are really farming, farming the cartographer chest). Farming the cartographer chest is more profitable than farming the map itself, especially on Very Easy Mode. The cartographer chest drops are dependent on the Luck %,GF%, Item drop % on top of the map description, above the map affixes. It is easy and it is fast.
So basically what I am trying to say is that don't do EP8(M3) because it is too hard, you should do lower , either epic/mythic 1/very easy mode, is a much better alternative, yes you won't have max item drop/gold find%/luck, but your main goal here is to hopefully get that crystalline hat/weap, eternalized weap/hat from that chest, in order to actually start your farming build. But check Codex to make sure the the items that you want do not require any specific modes+ before doing very easy mode.
After you reach a certain floor on very easy mode, you can then buy a floor level 200 map in EP8(M3), and convert it, which will increase the floor levels randomly, till you reach your desired floor level, say floor level 400 map, OR save your EP8 floor 350 map, and convert that to your desired floor level, after that you have attained that floor level, say floor level 500, after you have climbed to/reached it.
Also one last tip, start thinking of maybe getting some of the 100% ED legendaries and build a farming build around that.