Definitely speak to a lawyer . I bought a house 2 ISH years ago and my lawyer said they would set me up a company if I really wanted too, but strongly recommend I didn't go that way .
should be fine . I registered my first bike to a hotel in Chiang Mai on a tourist visa .
If you buy off a dealer they should help with registration ( for a cost) or private you can go to the DLT office yourself or most used car/ bike dealers will do it for you for a fee even if you didn't buy it from them .
If you have the money don't use an agent . You need to provide the same bits of paperwork for either so do it yourself and save a ton of money . Immigration are very helpful.
While your wife is in her home country make sure to get your marriage certificate verified both by your government and the local Thai embassy. Then when back in Thailand translated and verified by the ministry of foreign affairs.
We had a lot of extra stress not doing this before arriving in Thailand.