I was a bit daunted when I arrived in Thailand, but honestly it is not that difficult and like I said if unsure about something the helpful and very knowledgeable people like Brandon will always provide advice, if you decide to do it yourself.
I was quoted 35,000 Baht. This included opening a bank account.
I did it all myself for a fraction of the cost.
Opening the bank account is the tricky part, other than that it is just a case of following a simple process, filling in a few simple forms and providing the evidence immigration require.
It's your choice.
There are lots of helpful people in this group that will help with any questions.
I wouldn't recommend they live on any island as I think it would get boring, but they seem to want to. I think you are correct about Koh Chang being too small.