Closets tend to get disorganized and messy over time. This is because you accumulate more and more things as years go by. There is no reason why you should get overwhelmed though. You can pack your things in an organized manner piece by piece and you will eventually get done in time. Just make sure that you start early so you don't have to finish packing the whole closet in one seating. You don't have to allot the whole day just to get it done right away. You only have to spend an hour a day and do your daily chores as usual while preparing for move.
Get four boxes so you will have a box for the items that would be given away, thrown, sold and you're still undecided about. The remaining things would be packed. After sorting your things you would have minimized the things you need to pack. It would be easier to pack so you would be able to accomplish everything sooner.                 
To raise money for the move, you can organize a garage sale. This would be a great chance to get rid of the excess items. At least, you would really not lose them totally because you will get money for them.