I would say a bottom-up approach only works if everyone in the collective started the collective together, and were on the same page from the get-go. It's nearly always difficult and prohibitively messy to try to coalesce a government with a group of different people who arrived separately and at different times.
If you do have that chemistry where you have broad consenus without prolonged deliberation and debate and feel a bottom-up configuration is realistic for you, you probably want to stage visits or talks from professionals who have those skillsets and experiences which fall outside the range of your existing collective.
After absorbing the info sessions, you can have conversations about whether or in what fashion you'd all like to implement those roles or functions. Ideally, you will be able to access professionals in your community willing to liaise pro bono as consultants periodically to help you develop capacity.
~Cyclista Nicholas