I don't think you should BUY a domain name - you just basically "rent" them out for a certain fee every year. Some places do allow you to register a domain name and prepay for like 99 years or something like that if I remember correctly. Cant remember where I seen it, but i am sure you could find it if you look around.
You wont get ALL TLDs becaue you wont qualify for most of them - perhaps you meant most gTLDS ?I make sure no one can steal it later by buying all TLD variations