Does query string length matter?
does it would hurt performance


Not in any significant way. The initial parsing may take a little longer, as might the network transfer (though for hundreds or even thousands of characters you are not going to really see that unless you are talking to the server over a cellular connection or such!), but after that stage the query planner will be given the same tokenised statements whether you used table aliases or not. Time spent in the query planner's realm will be much more significant than the parsing+tokenising time, and running the resulting plan will usually be orders of magnitude more expensive again.

tl;dr: if there is a performance difference it will be practically undetectable.