1) ~6mo to recruit a team and agree on the broad plan. During that a combination of more comprehensive literature survey, meeting with the experts, investigating university research programs solving key problems which could be funded, etc. Concrete deliverables around a well communicated-to-public plan, simulation, etc., both of the launcher and application/payload.
Probably (to be altered): ~1y to recreate the subscale systems used at various universities, set up basic capabilities, etc. Obviously faster if I can just work with UW or one of the other groups. Another...2-3y to build the first subscale prototype capable of putting 1 gram into space (without circularization), but with a rocket second (and maybe third) stage.
Parallel development of the ~1m scale projectile, boost rocket, circularizing rocket.
Parallel development of LEO satcom payloads -- initial payloads inert, then maybe some remote sensing/beacon/etc. payloads, and suboptimal but research/commercial satellites. For a full LEO 1-3Mbps to the handheld terminal constellation, need frequency licensing, a lot of consumer electronics and specialized electronics, etc.; it used to be a 5-10y project even given standard satellites -- it probably could be done in 2-4y today. One huge advantage of low-lifespan LEO: you can rev the satellite design every month.
(Another option is doing the LEO satcom stuff in parallel using a conventional launcher at lower density.)
The full production scale system to orbit is probably ~5y after the first subscale to space.
(My real problem here is I have another much more practical startup which is unrelated, and in an area where I'm an expert, unlike this, where I'm merely interested. I'd rather do that, make money from it, then build this when I can at least contribute 3-5mm to it myself. So that pushes all of this out at least 3y and hopefully 5-10y. If I suddenly have a lot of cash, I'd probably be able to pay to have some of the earlier engineering work done on this, and if I had the right team, could probably just be an investor/boardmember.)
3) Kenya is probably the win (definitely Horn of Africa or South America; nowhere else is economically viable). Ethiopia also works. It would be done with full US ITAR compliance -- physical custody of the site, local construction and education, but no weapons proliferation. Ethiopia and Kenya are pretty solid US allies. I'd expect there would be a Bn or greater of host nation military/police assigned for outer security.
4) Ablative coatings, carbon/carbon structure. Only getting cheaper/better. I don't know much about the state of the art here, but it has been feasible for decades using older tech.