You need to book air tickets and accomodations for your first hotel before applying for a visa, as it's information required on the application. Contact the Thai embassy in your country of residency as Thailand has different rules for some countries citizens.
nothing is meaningless in the Thai immigration rules. Past performances influences future plans. A clean immigration record means you come under less scrutiny. Aquire enough overstay stamps and you're likly to get and undesirable alien stamp on your next exit.
Better develop Plan B if you only have 1.5 hours between connections. 3 hours should be the minimum you allow. Any minor delay, a long lines at check-in, and you've missed your flight. Do your check in online to save time.
I've been using a TR 60 for 6 month stays for the last 5 years. You will have to either extended for 30 days @฿1900 at the end of 60 days, or do a border run. If you extend once after the first 60 days you'll only need to do 1 border run. Otherwise youll need to do 2. Border runs are a good excuse to visit neighboring countries, although my favorite run is flying to Vietnam, Nong Khai Vientiane is the one I use the most.
Cambodia is the worst crossing point except for Myanmar. I've used every country bordering Thailand except Malaysia. Nong Khai/Vientiane Lao is my favorite border run. Always smooth. No problems with 2 turn around entries.
There's the official Bangkok rules, and then there's what actually happens. Requirements often depend upon what province you apply in, and the officer you deal with.