If your intention is to get a the 12 month marriage extension you don't require a Multi-Entry Non-O visa, just a get a single entry Non-O. The single entry is good for 90 days and you may extend it for 12 months after 60 days (during the last 30 days of the visas validity) and it will save you some money. Unless you plan to travel in & out of Thailand or you want to "test the waters" before making the plunge than a Multi-Entry will benefit you. It will also benefit it you if you can't prove a source of income. You will be required to make a visa run every 90 days until the visa expires. When the multi entry expires, you have several options:

1. Extend it for a 30 day tourist visa.
2. Extend it for 12 months based on marriage.
3. Apply for a Single Entry Non O outside of Thailand (Laos, Burma, Singapore etc).
4. Return to the UK and apply for another Multi Entry (based from what I've read you may only obtain this visa from your home country).

You don't say where your from in the UK, but from reading various posting on the subject the Royal Thai consulate in Hull seems to be customer friendly and you should be able to obtain a visa hassle free. Best to go to their website and do a little research, especially about work permits because you're going to require one if you want to work here......Papaguido....