Depends who your bank is in Thailand. Several (Kasikorn etc) allow ฿2mil and SCB allows ฿1.5mil so you'll have no problems sending 40k in one transfer.
if they want a lease then they'll accept whatever lease agreement you provide them. The bank doesn't set your lease agreement terms for where you live mate. Goodluck with your solution, hopefully it works. Maybe you want to share what you are trying so others in a similar predicament can also give it a go.
can't your partner (or whoever the land owner is) just write you a lease? Why do you need to put ฿5000 per month, can't you just put no monetary value or ฿100 a year etc?