IMO a 30' sounds ideal. We started at 30 ', then went to 34, then to 38, now want to go back to about 32'. 38' really is limiting to where you want to pull in for fueling, backing into RV sites etc. You just don't go zipping into places. Need to be selective to where you are pulling in.
If you plan to full time, then maybe a bigger fifth, but with a 7 year old ,thats going to be awhile. I would stick to a 30' for what you are going to do.
Arctic Fox is an excellent choice, somewhat heavy, but well built. Thats my next choice for a fifth wheel.