Just done this, and a lot of people tried to advise that bulkhead replacement is a better option- maybe they are right but I am happy with mine. If there are just small holes visible it may be worthwhile ie you have good footwells and centre panels. I could have got away short term with a bit of filler but decided to do it properly
Bear in mind you need to remove the roof/windscreen/doors and bonnet as a minimum.
Other than that i found it fairly straightforward. You need to be careful aligning panels and drilling the windscreen mount holes right (which I found a bit tricky)
Also get a set of stainless door hinge bolts/retaining nuts and some copper grease as I had to drill a stubborn one and use air impact tools on the rest.
Also for about half the price of paddocks try
www.yrm-metal-solutions.co.uk(not affiliated - just a happy customer)