First CoC Comet build, looking for help with next steps

All the comments are great but I would throw in another take. Just get more DMG and a headhunter belt. I got soul tether/fastmetabolism tech and I basically never use it unless I'm doing arbiter or some boss.

number 1 thing you could do for your defenses is get your 4th ascendancy, path to the ‘ES from body armour gives HP’ in your ascendancy, then switch to a pure ES armour with 900+ ES (should be a few div at most, more if you want more ES).

You’ll lose some spirit of course so you may have to sacrifice CoEA or blasphemy or convalescence but it’ll be worth it for the huge EHP boost, believe me. Blood mages get a ton of their health pool specifically from body armor ES so it’s pretty mandatory regardless of what build you’re going for.

I’d also recommend getting some sort of instant life leech, either from atziri’s gloves or from a heart of the well. (the gloves are better probably since it makes all crits leech instantly but you do sacrifice an armor slot for them)

Follow the good suggestions others posted. I just want to mainly add to them.

As a bloodmage i would suggest to convert mana cost to life, so use lifetap and atulis bloodletting in your skills. You already have life remnants and life leech from your ascendancy. You want atziris gloves for the instant crit leech. You also want high crit chance. I run my bm at 100% cc. Soul tether belt is great for recovering es, but you want one with the "lose %es per second" line removed and instill fast metabolism on your amu for the excess recovery.

If you dont mind following builds, may i suggest iamjustanthony as he does everything bloodmage and has budget as well as high end builds. You dont even have to follow any specific build, just use them for ideas.