Go to an approved driving school. One is called Myron. They charge approximately 1500 THB and they do everything. It takes 5 days to do but not 8 hours per day. They do practical and classroom instruction. They also do the testing both on bike and exam. Then they give you all paperwork to go to Land and Transfer office. Just go with a medical certificate and certificate of residence and pay the fee. EASY
One account only. The amount has to be 2 months before and 3 months after. Minimum balance can be 400,000 after 3 months. Each renewal you have to give photocopies of your bank book going back the previous 12 months. At Jomtien Immigration I had to bring in my updated bank book after 3 months of receiving my renewal.
For your first O retirement visa hire a Visa agent and let them do it for you after you arrive in Thailand. Sure you can do it yourself for 1900 BHT, which is a lot cheaper but an agency takes away all the hassle
For the first visa it can be better to go to an agency for the first one. It will cost you more but you will have less to complain about. Every year after do the renewal yourself.