You’ll only get 90 days on your Non O visa regardless if you apply at the Thai embassy in UK or the immigration in Thailand. Then you’ll need to apply for a yearly extension of stay which is not a visa but a permission to stay. If you apply at home before you come, it will be easier to open a bank account and apply for your extension and the process itself it’s also easier.
Non O immigrant visa is excused onward ticket requirements and you normally don’t have to upload any flight tickets, but why it’s asked for in the electronic application I don’t know. Just filled in some dates my self, didn’t upload any tickets, and got my Non O within short time without any issues.
Has to be in an account in Thailand but you can apply for the 90 days Non O visa at home and open a bank account in Thailand and transfer within one month for the one year extension of stay.
Some embassies and consulates were more strict when you applied for a tourist visa, but the requirements are formally the same but rarely checked in the immigration, but you might risk your airline will ask for an onward ticket within the initial 60 days, and as said the requirements are formally the same if you do get asked.
Non O visa and extension of stay based on marriage will allow you to get a work permit and that’s probably the easiest way to open and run a business together with your wife. I think you do things more easy by officially using her name and yourself as a employee.
Yes you can apply for a 90 days Non O based on marriage from the UK and do one year extension of stay based on marriage in Thailand within these 90 days.
If you’re not ready to apply for a Non O based on marriage from UK, it’s probably easier to come on a visa exemption and apply for a Non O based on marriage in Thailand as it’s not easy to change reason for extension of stay the first year. (From Non O based on retirement to Non O based on marriage) It could be an issue to open a bank account and bank the required 400K baht.