First Motorhome

I am going to buy a new motor home hopefully ordering it at the NEC in October. Had a caravan for a number of years but I have now finished work and my wife planning to finish in November so we have decided to try motorhoming and then do a lot of touring. The touring likely to be outside the school holiday periods if in southern Europe etc. So the questions.

Do people think it worthwhile getting air conditioning fitted to their motor home.  

The model we are getting has space for one 13kg gas bottle. How long is this likely to last if for instance we go away for 6 weeks and split our time between sites with electric and aires etc (is it worthwhile having a refillable gas tank fitted?) We are looking at getting a Chauson so heating is from diesel fuel. 

Anything else deemed a necessity that we can make sure we include when we order the vehicle. 

Thanks in anticipation of replies