One domain-two forks-separated communities

I want to merge two small, unrelated, and low intensity, communities into one domain.
E.g. "domain.com" (already existing) and "domain.com/OtherCommunity" to be created (more might come in the future).
My plan is to use a similar structure for both communities, e.g. more or less manually make again what I already have done once.
There is (for the users) no interaction between the two communities, rather the opposite (but isolation need not be watertight).
I really only plan a small button on the welcome page that reads "Continue to Other community"
(for those "others" that did not link directly to "domain.com/OtherCommunity")
All community members are basically known beforehand.
However, once logged into one of the communities, this community is what you see.
You see only THAT communities members, it's forum, it's image gallery etc.

My thinking is to use access control to limit access to "the other" community.
I'd appreciate any suggestions on how I should proceed.
The sites are not overly complex, neither will the traffic volume be high, but I hate running into some dead end halfway through.
A question - can I direct the users to different starting pages depending on who they are logged in as [Community or OtherCommunity?]

Any thoughts? Will my plan work? Any do's and don'ts that I should consider?

Best approach would be to just have 1 site, point both domains to it, and use usergroups/view access levels to limit access to certain community sections. Try not to over think splitting the 2 communities with a hard line in the sand as Joomla isn't really made for trying to have 2 entirely different communities under 1 roof. If you need a hard separation of communities then don't try to do this to begin with and just have 2 separate Joomla installs.

A question - can I direct the users to different starting pages depending on who they are logged in as [Community or OtherCommunity?]

Yes, that's doable.

Thanks,

As I am planning for more than two communities "under one roof" (all low volume and "not so valuable"), I believe that the solution with multiple Joomla installs would be to overdo it.

So, I take it that I will continue working along the lines that you suggest?

In that case yes I suggest just using ACL for separation, but again don't think of it as a hard separation of communities as some things you likely just will not be able to separate.