You must be a rich man, 250 rai of rubber. Fertilizer bill alone will be 1/2 mil Baht a year.
RIMM 600 are your tried and tested rubber trees, not a high output, but hardy, easy to grow and cheaper then most other clones. There are many clone types, some dry season tolerant, some fast growing, some lumber producers and other shigh yield.
Go see the local Agriculture Department, they will tell you which clones are doing well in your area.
Again cost will play an important part, some of the high yield Malaysian clones are in the 90 Baht a tree range and you are looking at around 20,000 trees. Jim