Check
this link. This is the home of the most modding tools you'll need. Make sure to download some script editor, WinBiff, IEEP, Infinity Talker.
You will also need
WeiDU dialog compiler.
Shadowkeeper is esential for character viewing.
NearInfinity (file viewer) is pretty good, but Infinity Explorer (from TeamBG) is better in some areas.
Other tools will come by time. You'll not need all of them immediately.
And, man, do step by step.

Making complete conversion is too early if you are new at this.