I would avoid a plan of overstay. With or without visa, immigration officers (IO) can deny entry for any reason. Despite what many may think or say, they don't really need to reason to deny you entry. A plan of overstay suggestions you don't care or respect the rules. Immigration officers love the rules. This may put you in a bad situation.
To the point about IO authority to deny you entry without a reason, maybe they can, maybe they can't, but do you really want the hassle
I hired someone to do all the paperwork, marriage visa etc. They told me a the time 3 or 4 weeks. It's been 4 weeks already and I am still waiting on my passport to get stamped. There were several holidays so they said it would be a little longer maybe 4 weeks..
In the past I have taken a copy of the house book, rental lease, photo copy of the landlord's passport signed by them and done it myself. Alternatively, you can use a hotel or agent and mis-report your address.
I would recommend getting a hotel for a week or two and find something long term once you arrive. I got an AirBNB near Kamala that really sucked for 2 months. The place was good, the location was good, but two months was too long for too quiet.
I like 'The Senses Resort & Pool Villas Phuket' good facilities decent price next to everything but not in everything. 3 minute motorcycle ride to the beach, great view
bahtsold has several businesses for sale. Of course if they were truly profitable - why would they be selling them. 200,000 baht is enough to buy visas only.
I use google/flights - but I dont have specific knowledge of one day being better than others. Google flights allows you an option to see a grid of arrival/departure.
I dont used cars too much, especially out on the street. There is often a service charge and it seems my cards are often use fraudulently. It seems I have to replace them once a year.
If you have the cash - I would recommend using it.