Yes, I totally take your point! I always forget how frentic things are in April/May too - you probably don't need the extra work at that point in the season!
And oooooh a Rhino! I don't think you'll be disappointed book - I love mine! The base is really great - you literally just bolt it down.
The height - in the range I bought, which was a fairly basic one (Harvest I think), the eaves height was a bit higher than on other makes. I can't remember whether this was just how it came or whether I paid for extra height... I remember it being something I did quite a bit of angsting about. DH is over 6 foot and we wanted him to be able to get in and out without any bother.
Rhino do go to some of the RHS shows - I saw mine at Malvern - and they sometimes have super-special offers (really a lot cheaper even than the January sale) if you have transport to take away the greenhouse on the day. But I think it's a bit chancey if you get the thing, IYSWIM. You could ring them and see which ones they'll be attending? I guess if you're not ordering to October, it gives you a chance to view and decide!
I really struggled over the coloured frame. It's very pretty and all, but it's a lot of extra ££ for a colour.
Dimensions... mine is 6 feet across and there is quite a decent amount of space for a row of staging either side and then room to move in the middle. If I had space, I think I might just be tempted to go for a longer narrower one and then leave a gap on one side if I needed a bit more of a turning circle or potting room. But this is driven entirely by greed since it would be all about cramming in maximum numbers of plants!!
I'll see if I can get a picture as it might be helpful!