Assuming you live in Sacramento proper and not up in the foothills somewhere, and assuming you mean the American River bike trail ... 8 gears is more than enough. There's a decent hill on the bike trail as you get up towards Folsom, and there are some overpasses here and there, but I mostly ride out there on a single speed, and even when I ride my road bike I tend to use only a couple of gears. I am not a strong rider by any stretch of the imagination ... it's just a really flat trail.

A hybrid is not a bad option at all for around town and on the bike trail, although I started to hate mine pretty quickly because it was so slow and heavy ... it's a lot of work to get very far on a hybrid, so you ride the same stretches over and over and it gets a little dull. You might do better with an entry-level or used road bike.

It's too bad College Cyclery on Freeport seems to be under new management -- they used to have a very nice selection of used road bikes, but the last time I was in there it seemed like it was mostly a bunch of old Schwinn cruisers (many marked "not for sale"). Bicycle Chef sometimes has used bikes on consignment but they tend to be fairly high-end stuff.