Based on a Google search, it is my understanding that POTUS post-election PAC fundraising is in the hundreds of millions.
Does PAC and campaign finance law permit (or prohibit) the money to be used to buy rooms at POTUS owned properties or other similar transaction with the POTUS' familial organization?
In general, there is no current law requiring POTUS to divest himself of investments. There is no Presidential Conflicts of Interest Act, and existing laws do not apply to POTUS. The closest you can come is 18 USC Ch. 11, which does not prohibit doing business with a family member. Or, here is a proposal, which vaguely approaches what you are looking for, requiring POTUS and VPOUTUS to "divest of any financial interest posing a potential conflict of interest by transferring such interest to a qualified blind trust", but even that law would not prohibit a third party from renting rooms in a facility which POTUS has an interest in.
