New to cycling and this forum. I just bought a CAAD 8 Claris (8 spd) as my second road bike. Two questions -

1. Is it worth it to upgrade from Claris to a used Ultegra group being relatively new to cycling? Has about 2-3k miles on the used group

2. Do I have to replace the crankset as well? The person is selling cassette, shifters, front and rear derailleur, and brakes.

Thanks for the help, be sure to be as sarcastic as possible with your criticism!