MBB -> VC path

From what I've heard/read, VC recruiting is much more unstructured - is signaling to recruiters/headhunters you're interested in exploring roles the best path? Similarly, have heard interviews are more unstructured - what should be expected here?

Yes, VC recruiting is incredibly unstructured and largely indexed on two things - your network to source/diligence and your quality of thought on original businesses.  I worked at vc firm where the common view was that vcs were generally unknowledgeable and could only help with hiring and fundraising, but the former is of utmost importance.  

There are two vc headhunter networks that are very active on linkedin if you search briefly, as well as a couple search firms that contract pretty frequently with the tier 1.5/2 firms.  The tier 1 firms recruit mostly on internal recommendation/networking.  For the headhunters, happy to say over dms who they are.

I'm sure varies by firm, but how does day to day / week to week vary across sourcing vs. diligence vs. portfolio help?

Ironically I think that venture is a power law game as well.  A lot of people view VCs as an attractive exit opportunity and coast by with 40/55 hour weeks which you can certainly do for years as it takes years to recognize whether you're a good vc or not.  The top 10% of VCs often don't seem like VCs and often do things tangentially related to get to 70/80 hour weeks - when you work an industry based on power laws - you need to do anything humanly possible to lay as many nets as possible.

You diligence as much as needed to build that muscle and build trust with your GPs that you can help champion their stuff.  You do portfolio as much as needed to make sure your investments work out and look good.  You spend the rest of your time sourcing as that's the only thing proprietary about this industry that'll never go away.  This is, evidently, not spending your time on PB and CB just looking at startups - this is something everybody does differently.

One of the major perks of MBB has been the coaching / professional development - to what extent does this culture exist in VC, and is it emphasized more only at larger firms?

YMMV at different firms :).  This is probably something you want to index on in the interview process and suss out.  Some large VCs (2B aum can actually have rly good coaching processes) so its not directly tracked to small/large firm.  I would rec Mike Dauber's article here on associate hiring.

WLB - working ~9am-10:30/11pm or 60-65 hours/week has been my experience on avg. at MBB (with fluctuations), how does this compare to VC averages?

Similar if you love the job, if not higher :).  I think the work and things that you'll do to get to that level are miles more interesting, though, than what you'll do in MBB.

Compensation - as a 3rd/4th year at MBB you are making ~$225-250K total comp, obviously carry is much later addition to comp but how does that compare to pre-partner positions in VC?

If you're starting off as an associate in VC, you'll likely take a bit of a haircut, maybe with carry expected to carry the difference.  Things are different at the senior associate/principal level thouhg ~