you just fo through immigration and show them your visa and you will get stamped in, no need to go any where else. Is this an extension on your type O visa? if so you will be stamped in for the full duration of your extension? If it's the first time you have used the non O it will be a single entry and you will get 90 day stamp, if you want an extension then you will need to open bank account etc. In your first week so you have time to meet the requirements. If the type O retirement isn't extended then after 90 days it will be used
Which retirement visa have you got? Is it a type O-A visa ? 12 months? Or a type O visa 90 day?
If it's an O-A visa you will enter thailand show them your e visa and you will be stamped in for 12 months or up to your insurance due date. If it's a type O based on retirement you will get a 90 day stamp
i would suggest so that it is easy for you that you use a family members address for your bank statements etc. So they can send you any details. It also if needed have somewhere to pop back to to fill out your new visa application. This way you will have your bank details with your uk address
Far too hard when you can simply visit a neighbouring country and return resetting your stay. Not sure why you would want to put yourself through this when there is just no need