Welcome to TBN:
Parts are not something to worry about, Mahindra has been involved with the U.S. since WWII and in the tractor buissiness since around 1960. As Dave said, they are the 3rd largest tractor manufacture in the world, there dealer network in growing strong. As far as resale i think alot of people who bought Kubota's when they came into the country thought the same thing. We have only had 1 used Mahindra that a customer sold because of a family issue, had it fo approx a year had around 50hrs on it if i remember correctly and he lost 1,000 on it i don't consider that too bad. I think you'll be happy with a Mahindra, we have sold quite a few 6000 and 6500 tractors out there and everyone has been very pleased.
Tractors also have been very reliable.
Good luck with your purchase.