do you have a budget for it, as cheap as, money no issue, or somewhere inbetween...you say you have built cars before what are your skills, if they are in welding it isnt too big a job to copy the independant suspension set up of the kit cars then you can have the right width for the rear without multiple spacers and or wheels with massive offsets. You will also need to extend the upper mounting points for the dampers to keep them more or less vertical to ensure smooth action of the spring and damper...not essential I guess but steering geometry is complex..
The front will be more tricky, are you going for frp front end, you will need the special drive shafts the lower wishbones and the track rods, the suspension is set up differently too but I guess you will be using your own suspension units anyway so you will just need to get the right set up.
you will have a load of fun with this, are you planning to do UK Club rallying or rally cross or something else.