So I haven't really gotten too much into the PC version of Morrowind in about five years (although I put hundreds of hours into the xbox version). I tried to get back into the game recently with the Overhaul 3.0 and had horrible HORRIBLE frame rate issues while outside. I have a very good laptop and I've tweaked with the settings for days now and I'm about ready to give up on the mod. I've put about four hours into a character that I really like and was wondering if when I get rid of the overhaul will I still be able to play my character on vanilla Morrowind or will I have to start over?

Two other questions:
1. What's your very favorite mod? I just want to try one or two since I very rarely use mods when playing games.
2. I'm confused about Tamriel Rebuilt. I know it's a mod designed to make the rest of Morrowind and that they have three or seven/eight areas done. But are they just different islands at the moment? I'm not sure how it works because the work that's done are areas apart from each other.

I really appreciate all the help I can get.
Thanks

You should be able to completely uninstall MSGO and still use the same Save file.
MSGO is mostly replacers, which has no bearing on a Save file. Although this does largely depend on the Options you chose.

But either way, I can't think of anything in MSGO that would cause problems for a Save file. Just be sure you also Update and Repair your save file with Wrye Mash. Which is standard practice for adding/removing any mod mid-game.

Morrowind is an old game, not designed for modern PCs. Most people can run a modded Skyrim better than a modded Morrowind.
MGE's Distant Land, any shaders, and animated grass are the main killers of performance.

TR is the (currently unfinished) mainland of Morrowind.

http://elderscrolls.net/morrowind/tamriel-rebuilt/images/main/Releases.png is probably outdated, but basically Telvannis, Antideluvian, and Sacred East have been officially released.
That is a huge chunk of land, with lots to see and explore. It's not just "different islands" floating out in the sea.

There are other Alpha releases (very unfinished areas) that are also available, and I think that's what you're asking about. But those areas are more like showcases, not exactly suited for you to take your character and expect to have adventures.

Tamriel Rebuilt will eventually become one continuous landmass. This is how the map looks if you combine the TR mainland, the recent Alpha release, the city of Almalexia and some as yet unreleased Redoran lands including Baan Malur ( aka Blacklight): http://imgur.com/LHRz4Qp. You can go from Baan Malur to the top of the Telvanni lands without having to swim or levitate.

Basically what Pluto said, but if you have missing resources after MGSO is removed then you need to use http://download.fliggerty.com/download-58-633 to re-register Tamriel Rebuilt.bsa just to make sure the resources are in place in-game.

The original http://mw.modhistory.com/download-4-5212 cannot re-register BSA unless you edit Morrowind.ini in the archive section by removing the same line shown below and save it then run BSAReg.

[Archives]
Archive 0=Tribunal.bsa
Archive 1=Bloodmoon.bsa
Archive 2=TR_Data.bsa