Im after some advice as I'm not sure where to start. Hope you guys don't mind me asking a whole swathe of questions.

We had planned to purchase a Chinese CNC however this may no longer be an option so I'm thinking of building one instead. I've built a couple small machines but I seem to be hitting a block with a big unit. Extrusion and VWheels seem alot easier lol. The router will be 8 X 4, ideally 5 x 10 would be better as we work alot with 5 x 5 sheets of Birch Plywood but I'll go with what we can get. It's going to be used for MDF and Plywood production type shape cutting as well as 6mm 8 x 4 plywood sheets long sweeping cuts. HDPE, Plywood, MDF, Hardwood, soft wood and Ally machining for signage. The v carved or pocket cut type. I've also got an idea for machining 100mm thick laminated birch Plywood blocks into 3d (2.5d?) shapes.

I've had a read through of the stickies and build logs but there are a couple of bits which are making it difficult for me to price up...

Machine size

What short of frame would I be looking at for the above sizes? 3 X 1.8m would be good enough for an 8 X 4?

Bed/Stand

Does this need to be made from steel? Could I get away with making it from 4x2 with a 40mm MDF top?

Frame

I've not welded since school but reckon I can weld together a frame if I have a bit of practice. Would 80 x 80 x 5mm steel box section work? I picked 5mm to allow for tapping. I'll get a design made up but currently I'm thinking of 3 long sections with 2 end pieces and 4 supports left to right, one every 600mm or so.

Square rails

Will 20mm rails work? I've only been able to find these at 2.7m so does that mean that 8 x 4 is the biggest I can go? I would be looking at Hiwin.

Drive system

25mm ballscrews, was my first thought but again, I'm still learning. Is there is a good quality supplier to get these from in the UK?

Electronics

I'm still learning about this. I've been reading stacks of posts from Jazz to try and get the right balance between cost and performance. Hoping someone could point me in the right direction in terms of specs or reading material. Fully understand I need to get the mechanical design sorted.

Spindle

I'm thinking 4.5kw with a 6kw inverter to run it. This is the sort of spec we were looking at in China. Is this overkill for what we need?

Software

I've seen alot of good to be said for UCCNC so I'm thinking this is where I will be edging towards unless I'm off the mark again.

Budget would be up to £5k but ideally lower if at all possible. Does this sound doable or am I way off the mark here?

Please feel free to correct me or ask any questions you need answering.