My wife got tourist visa to UK quite easily before we were married. I was on Ship she sorted it all out just followed all the steps as per British embassies website. Took about two weeks
I fly in and out all the time for work have lived here since the early 90s. Pre covid was rarely asked by check in staff now i would say I get asked to show visa or ticket about 75 % of the time. Its actually AITA regulations to ask for showing onward flight. In all those hundreds maybe thousands of entries i have been asked to show onward flight by immigration a grand total of 1 times
you get 60 days upon arrival so dont need visa. Where to stay also depends what you want to do Bangkok is big. I personally like IBIS riverside nice clean rooms, great location and good breakfast