The respec isn't really that hard. Unless it was changed you get two respec points per act in each difficulty. With a little planning you shouldn't really need more than 12 respec points if you mess up. There are also orbs of regret, a one use one respec point item, which you will get as loot or can buy. There's always a respec option, at times you may need to farm/buy respecs, but you'll never be locked in to your decisions entirely. As for server restrictions, no. Your character is locked to your league and that's the only restriction I know of. At the moment you have the choice of default and hardore (aswell as daily community events, which aren't permanent). Further down the road however more leagues will be introduced however, such as world pvp leagues etc.