Thanks for the comments, everyone, and the specific suggestions of appropriate curriculums and other relevant forums.
We're just talking about elementary school at the moment (even if some subjects are or will be done at higher level), so some concerns such as official grades, facilities (e.g. science labs), expert higher level subject teachers (hypotheticaly, at least), can be bridges we'll cross when we come to them. We can possibly switch to other schooling options later. The expectations for elementary school are so minimal, it seems virtually impossible to fall short academically with highly able kids.
There are other concerns such as children being able to be focused, resilient, efficient, having a work ethic, and so on. But I don't see any one of home school or virtual school or various kinds of B&M schools being clearly better or worse in these regards.
Timewise, we have the freedom to go travelling during school times by getting ahead of the schedule. But unfortunately we are finding it time consuming for both parent and kid, for various reasons. Hopefully with pure homeschooling we can focus on learning rather than doing, and not worry about the progress monitoring, work samples, practice tests and so on.
By the way, where we are, to homeschool, once a year you just tell the department of education "we're homeschooling this year". That's it. Done. No monitoring, no scrutiny, no testing, nothing.
A huge concern is cost. The virtual school is free (to us). The state pays the curriculum provider (k12.com in our case) way too much for what is essentially homeschooling material that is mediocre at best. Then the virtual school itself (a separate entity to k12.com) has its own staff and teachers that provide a combination of help and hindrance for no net gain. If only the state would give us a fraction of that budget directly to us to cover our own homeschooling costs, but that won't happen. So to homeschool independently we'd have to pay $1k per kid per year? $2k? More? With 3 kids and one 5-fig income, the costs could seriously carve into our budget. It could be money very well spent, or it could go badly. The cost-benefit analysis has to beat our current "free, and almost tolerable". Or maybe it's worse than "almost tolerable" and we just have to homeschool and figure out how to pay for it (save less, work more).
