The steps are quite simple.
First make sure your contract has ended. Then, go to Tmpoint, mention that you want to transfer your Maxis fibre to Unifi. Usually they will give 6 months free bill, depend on which plan you select.
Complete your Unifi registration and TM will give you transfer ID. Call Maxis, inform you want to transfer out, provide the transfer ID to them. Pay any outstanding bill if you have.
Wait few days for Maxis to approve transfer. Once approve, TM will arrange technician to setup Unifi at your house.
Maxis will terminate your fibre account within 2 weeks time once Unifi is installed. There will be another final bill prorated for your Maxis fibre. Pay that bill and consider it done.

Yes, it is applicable the same way regardless you transfer from Unifi, Maxis, Celcom fibre etc as long as it run on TM HSBB infra.
Those who terminate without going through the transfer process risk losing their port, especially if your area has someone in the waiting list. Once you terminate, the port will be assign to the next in line, and by the time you want to register another ISP then no port for you.

Usually there are different offer. For example x month free or free speed upgrade.
Just like offer for switching to Unifi, either you get x months free or free TV.

Not like that.
You apply Unifi through agent, tell them transfer from Maxis. Agent will give you transfer ID upon registration.
You just need to wait Maxis to call you for confirmation/offer, if you agree to the offer Maxis will reject the transfer. Should you choose to proceed with transfer, Maxis will approve the request and Unifi team will set appointment for installation.
After Unifi installation, your Maxis fibre account will be terminate within 2 weeks.

1. It is automatic. Your Maxis account will run for 1 or 2 weeks and then it is terminated.
2. For refund, any amount less than Rm30 you have to call their customer service. Can also refund to your Maxis postpaid account if you have one.