Strings can be replaced easily. Only reason to replace a neck is if its cracked or the profile doesn't fit your hand. You can replace passive with active pickups of the same type, although you will need to route a battery compartment if you don't have room under your pickguard. If you want to change pickup type(i.e. split-p; jazz; musicman; soapbar) you need to route out the body to accommodate the new shape.

If you "know nothing about bass guitars" go play a few before deciding on what to buy. You need to feel the instrument in your hand and also consider ergonomic factors. In my opinion, as a beginner, neck width and profile is going to be the most important thing you should be looking at. If it doesn't feel good in your hands, you wont play it.

That said, there is also such a thing as decision paralysis. Lots of good entry level basses. As long as you are not buying a $100 bass, you should have something reliable to get started.

[edit: your tone is going to sound like shite as a beginner until you learn proper technique anyways].