A 31 gallon fresh tank is pretty typical size, and should serve you well enough.  That TT is 22' long overall, a decent size.  There may be times when you grow tired of looking at each other's faces over the single place to sit (dinette), but anything with a sofa added in will increase length a fair bit.  It has plenty of cargo carrying capacity (weight wise).  Looks like they vent the fridge through the roof, which is far better for proper function than sidewall exhaust.  Winnebago has been around for a long time.  If you like it, go for it.