First Trip...!

Hello all,
I'm flying LGW-LAS next month. It'll be my first trip with VS and also the first flight my 3 year old will ever have made.
We're going to be crammed to the rafters with excess baggage as we're moving abroad with work for a few years, and I thought I'd ask here if anyone had any advice for making the flight as relatively pain-free as possible; especially with a youngster?
I'm a bit worried reading reports across the internet of thin seats with poor seat pitch, although I presume if we manage to get seated together we'll be able to pop armrests up to make ourselves a bit more comfortable.
So does anyone have any tips? Is an upgrade to PE for a family of 3 affordable, or are you ever likely to luck into a free one? How about securing decent seats; are extra legroom ones available for pre-booking, or only on arrival? When should I try to check in? Will we be guaranteed seating together bearing in mind we're with a 3 year old? Is there a lounge at Gatwick either for free or that we can pay to use? As we tend to only fly around the UK on locos, is the flight likely to be full to bursting?
Sorry for the list of questions but I'm keen to try and make it a pleasant experience. Any advice would be welcome!
I'm flying LGW-LAS next month. It'll be my first trip with VS and also the first flight my 3 year old will ever have made.
We're going to be crammed to the rafters with excess baggage as we're moving abroad with work for a few years, and I thought I'd ask here if anyone had any advice for making the flight as relatively pain-free as possible; especially with a youngster?
I'm a bit worried reading reports across the internet of thin seats with poor seat pitch, although I presume if we manage to get seated together we'll be able to pop armrests up to make ourselves a bit more comfortable.
So does anyone have any tips? Is an upgrade to PE for a family of 3 affordable, or are you ever likely to luck into a free one? How about securing decent seats; are extra legroom ones available for pre-booking, or only on arrival? When should I try to check in? Will we be guaranteed seating together bearing in mind we're with a 3 year old? Is there a lounge at Gatwick either for free or that we can pay to use? As we tend to only fly around the UK on locos, is the flight likely to be full to bursting?
Sorry for the list of questions but I'm keen to try and make it a pleasant experience. Any advice would be welcome!