Firt news: No prolem or going to Mrauk U.
No government permit is necessary.
No travel agency arrangement is necessary (just, if you like to be packaged by a travel agency).
Don't believe to most travel agents in Yangon. They simply don't like to plan trips there, and they are aimed to redirect ou to other destinations.
Sittwe is completely quiet.
Mrauk U is simply fantastic. No tourists (we met last week no more than 4 people). Untouched environment and people. Tens of temples. They resemble those in Bagan, but are more fascinating in some instances, sincethey have not been 'restored'.
I suggest to skip Chin villages: very few old tatooed women and villages like those you can find close to Mrauk U (and 2.5 hours of boat).