With so little in the way of existing body to use as datums it might be best to go for heritage panels wherever possible. If not, then get them from M-Machine or Somerford Minis.
That is certainly a lot of welding, but the good news is that all the panels you'll need are available except, if needed, the top of the front bulkhead.
Get a set of solid sub-frame mountings and bolt it in solidly after first fixing the front toe-board sub-frame mounting area first. Then the sub-frame can be used to line up the inner wings & front panel before starting. From there you can align the A-panels, scuttle panel and wings.
It sounds a lot, but once you get into it you'll find it straightforward.
As 'sonix' says, you don't need a spot-welder, but make sure you have a powerful MIG with a long duty cycle. Do lots of check assembly before welding.
M-Machine do a very comprehensive on-line catalogue and their delivery service is superb..