I think having a tranfer window is a good idea, but I don't think it will play out the way people think it will.
Someone posted the scenario of a 3 QB competition to be the starter where 2 wind up in the transfer portal. When these young men enter the portal, they are likely no longer with the team. Having a transfer window isn't going to keep them on the team. They will inform the coach they intend to transfer when the portal window opens and withdraw from the team to keep their eligibility. They're not going to burn a year coming off the bench for mop up duty. Otherwise, they wouldn't be in the portal.
So, having a portal window won't decrease the number of transfers. It will make the coaches life easier to only have to manage the transfers within said window.
I don't agree with just one transfer. There's no reason to tie a student athlete to a school.
If an athlete doesn't play after transferring to a school, why should they not be able to transfer somewhere else? Who are they hiurting? If they do play, they could still transfer, but would have to sit out a year. So, that old rule still works.