I like the idea of a crew cab and I saw your truck in the forum, will need to do something soon as I have two sons, a 3 year old and 4 month old so I don't know how they will both fit in (unless I modify the pedals so the 3 year old can reach them as his driving and steering is spot on and I'll sit in the back!).
Another mod I've thought of is wouldn't mind being able to turn it 'off' the hydraulics and not pump oil around when I don't need it, as for a high speed pto to which could drive the hydraulics can that do it?, I think I have one on another gearbox, if I take a picture of it can you help identify what it is?
As for cost, I don't spend much apart from lots and lots of time, the 406 was £2850 with the addition of a LWB chassis, cab, gearbox and axles which was nice, but the guy listed it on the Friday before Christmas day with poor spelling and pictures so all I'd say is save your money and search at Christmas!, so don't worry Nick, use the power of ebay and 'saved searches'!
The sauer danfoss valve block was in exchange for some plastering, (had to buy the joystick, again you can guess where from Ebay Europe somewhere) and I'd recommend it as you only have to wire the joystick to the valve block and happy days (although it's a 24V unit), really nice not to drip oil everywhere when you disconnect the quick release couplers, I wouldn't buy one outright as their +4K new, but I did manage to pick 2, 4 spool proportional parker valves up off ebay recently when a guy didn't know what they were (one's for the crane remote control project, other spare).