At that fabric store, ask if they have a pattern pack for a hooded jacket and buy it. It'll tell you how much fabric you need according to how big you want it plus shapes on paper in which you pin to the fabric and cut around so you have the exact pieces you need. It also has written instructions with steps.
I wouldn't reccomend insulating your sweater as it will make the job considerably more expensive and challenging. Besides, your hoodie should really only be used for warm weather.
Thumbholes are definitely not reccomended. They are very hard to pull off for a 1st time sewer because they require a skill that even I don't know.
Again, if you have a pattern pack, it can explain how to do ribbing properly. But if you don't, read Malcom's explanation.
Now Ihave a question for you: do you want a zippered or zipperless hoodie?