Ditto the above comments. No preamp needed. The most vital part of the path going from tape line level out to your computer is the analog/digital converter. That is part of your sound card. These come in various levels of quality, and a high quality one will make your recordings sound the best. But I would not invest a lot of money in one for your stated purpose, because your tapes are probably not super high fidelity recordings to start with, so "garbage in / garbage out" holds true even with the greatest D/A converter. A decent consumer grade sound card like you probably already have in your computer will probably be fine.

After your are on your hard drive in digital format, one of the "vinyl restoration" plugins might be just the ticket. For example, if you can isolate a section of background hiss without any superimposed music, some plugins allow you to identify that as noise, and remove same from the entire recording. In my experience, this works great, with very little harmful effect to the overall sound.

You will have fun doing this project, and will learn a lot.

Al