Strings are not really memory intensive, each char usually only exists out of 2 bytes (supporting every language) , the only reason why you should use shorter strings then longer ones if you are doing certain operations on them, because a string is generally just a array of characters and with bigger strings, bigger operations have to be done.
so in general, reserving 100 characters for a string results in 200 bytes which is 0.2KB , and with 1000 strings this is less then 0.2 MB, so this shouldn't really be any problem unless you are storing everything in RAM on a mini computer with 256MB ram.
Answer: Not a very big effect on size (realistically seen), medium effect on performance (in nanoseconds) because iterating each character and for example comparing with another one in a long string can be relatively intense, but nothing to worry about untill you are comparing thousands of strings with thousands of other strings