Those people with their horror-stories are just dumb. They would have run into trouble anywhere.
Buying land and build a house is actually very easy here as you don't run into all those complicated permits etc like in EU or US.
If you buy a property, you can not do so in your own name, but thete are many legal ways to secure your future. Lease or usurfruct are the simplest ones. With a usufruct you can do anything you want until you die. The official land-owner can't even enter the property without your permission.
And all this costs... zip, zero, nada. OK, 10 baht stamp-duty.
So, don't worry, do your due diligence, just as you have to do in your home country, and enjoy the simple life in Thailand.
This is my house. Build it myself (with some hired labor).
With a non-immigrant O visa (mariage or retirement ?) you have an initial 90 days.
Before that time is up, you can extend it to 1 year.
To do so, you need a certain amount in a Thai bank account (400K if mariage, 800K if retirement), and some other stuff.
You best check the immigration website or go to an immigration office for a complete and up to date list.
Extention costs about 2K.
(All amounts in Thai Baht)
After your visa is extended to 1 year, you need to show your face at the immigration office every 90 days (called: 90 day reporting) to re-confirm your address.
You can also do this on-line at the immigration website.