Conversion plans

Since september I've spent countless hours on the Internet looking at conversion companies and ideas. Sometimes I think we should buy all the bits and bobs and do it ourselves - I've been looking at secondhand seats, kitchens and stoves, and also new 'off the peg' campervan units - but then I remember how little time we have on our hands, and how few practical skills, and wish I could just give it to someone to do it all for us!
I think we'll probably end up with somewhere between the two, doing some of the work ourselves and using professionals for the rest.
There is a company in St Ives near Cambridge who look interesting. There seem to be a lot of campervan companies in the West Country and on the South coast, unsurprisingly I guess, but not much up here. I've been in touch with a company in Essex a few times, but I quite like the look of the things the Cambridge company have done - more bespoke and less modern-MDF-blandness. It's hard to tell from their website whether this is the sort of project they do - it looks like they're more on the upholstery and soft furnishing side rather than the welding and carpentry side - but I've sent them an email to see if they might be interested, and I guess I'll just need to see what they come back with. I also have no idea at all how much it would cost to get a company involved - some of the big modern VW conversions seem to cost tens of thousands of pounds, which is just not going to happen!
I've come up with a provisional layout plan which I think will work, but it would be very useful to get a professional opinion! I think we should have 4 individual seats, two forward-facing and two rear-facing - it's not really wide enough to get two seats next to each other anywhere without restricting the movement from front to back - how many times I have wished for a side door like most campervans, rather than the rear doors! The wheel arches are right in the way on each side too...
Anyway, in my grand plan, these four seats, plus the tables which will sit between them, will convert in some clever way into a double bed, a bit like the arrangement in a narrowboat with a dinette double bed (fond childhood memories of many of those...) Behind all this will be a kitchen area (sink, fridge and hob) and storage. However, at the moment I don't really have a plan for where the children will sleep - minor detail! I'm thinking maybe some kind of hammocks acrossthe width of the van in the rear kitchen area, or maybe in the front cab somehow.
It would be great to have a pop top/elevating roof one day, but I have no idea what that would cost or involve. It would give us more headroom and also some more space to fit bunks, but I doubt it will be in the budget for a while. I think we should probably have a go at using it in its current configuration before we make that commitment.