Welcome to BladeForums!! Be advised that making knives is an addiction and uncurable disease!!!!
Teak is an oily wood and sometimes does'nt glue well so scales on a full tang knife are only as good as your adhesion. You really have to rely on mechanical fastening [pins,screws]. Other than that, Teak is about as durable as you will find. Resists rot, resist bugs and is very stable moisture wise. If you can walk on it for 20 years, I don't think you'll wear it out on a knife handle!!
To finish just sand out to about 400 grit and polish. If you try to put a finish on it, I would suggest an oil such as Teak oil, boiled Linseed oil or something of that type. Give it a try!!