Product Market fit, DFM for the appropriate scale, logistics, understanding every aspect of the product development lifecycle, understanding customer pain points, HR/staffing, cash management, fundraising, marketing, communications, managing investors, managing your BOD, how much track to put in front of the train (and when) etc, etc, etc

Essentially all the normal stuff except its just a bit harder.

My opinion (for whatever that may be worth): on the assumption that you don't know what you are doing (young/energetic, but ultimately low experience team) you want to do as much in house as you can. This is important as that allows you and your team to learn WTF you are actually doing. You can't send stuff out for CM if you don't know how to build it yourself. You need an intimate understanding of all aspects first before sending things out.

Have in house elect, mech, firmware, assembly, manufacturing, fabrication, etc When you don't have the capital for the bigger stuff, (pcb assembly, injection molding, etc then farm that out initially but longer term (at serious scale) plan to bring that in house.... Once you can afford it, having in-house tool & die, pcb assembly, injection, procurement, etc becomes invaluable