I am currently 78hours in a play through of New Vegas, and I was wondering if buying the Ultimate Edition will allow me to use that save game in it.

Yes. The Ultimate edition, IIRC, is literally the game and the DLCs in one package. Theres no additional content or anything like that.

Technically, it does give additional content, but you should be able to access everything with your current save. Not sure about the Pre-order packs- they might kick-in on a new game. But then again, the equipment given tends to be better than starting gear, but won't last too long.

Old saves totally work fine with all the new content. You'll continue on from wherever you are with way more items and quests to choose from.

The new quests get added to your PIP-Boy for the DLCs. For Courier Stash and Gun Runners Aresenal, all new items get added to player inventory and to the shops when you load your game.

Courier Stash might leave you encumbered, there's a lot of items that go into your inventory, including four sets of armor that when combined weigh a lot.

YES, YES, YES AND A BIG FAT YES.

cool I guess I may as well buy it right away.

After installing the game, and starting up your old save, wait a few minutes and let everything load. You'll get messages about stuff being added to your inventory.