Your English is pretty good compared to some others. If it's your first time to Thailand you'll likely not be asked for a ongoing ticket but if you know you will be leaving at a certain time, be good to get it before you face immigration
you'd have to either get a metv 6 month visa or do a setv for 60 days, a extension, a border run, a 2nd extension and a 2nd border run in that order for a 6 month stay. If you did this after spending considerable time outside Thailand then I doubt you'll have issues with immigration denying entry for living in Thailand on tourist visas etc