I have taken all of my kids when they were 4. In December, DS2 was 4. Here are his thoughts on your list:
1. Star tours - liked it
2. Soar'n - LOVED IT!!!
3. Splash Mountain - didn't ride because it was too cold.
4. Barnstormer - LOVED IT!!!
5. Test Track - LOVED IT!!!
I didn't take him on Big Thunder Mountain RR. I was worried about him hating it and then being scared/difficult the remainder of our trip.