With a replica, it depends what type of replica you want to do, there are many option bearing in mind that you are not going to war with it or you are going to run the guts out of it once its built. So you don't have to use thick armour plate just mild steel plate and not as thick as long as the original construction is strong enough ie the hull and wheel stations are to a standard as not to fall to bits. As for the interior detail you don't have to do too much detail as long as the outside is spot on but that depends what you want out of it. Or you can do a faithful original.
The hull turret and fabrication work needs to be put on CAD so the parts can be cut out with a water jet cutter, laser or plasma thus saving time than doing it by hand and a pile of cutting discs years later. All the cut parts will be like a airfix kit that needs assembling. You can rivet as per original, the holes pre cut in the CAD process or you can weld in place and use cosmetic rivets as with Guy Martins WW1 replica.
With the wheel station it means replicating the amount of wheels you need and suspension bits shocks you need which can be used from modern day vehicles which will be hidden from view and perform better than original plus the weight of the total build will be less as you don't need thick armour plate which is kinder to the wheel stations and track. The road wheels can be cast aluminium or you can fabricate from steel a much stronger replica wheel. The tracks would be on the tricky side but not the end of the world, there are many options for that. Power and transmission is endless, find a reliable easy to maintain engine and box or you can hunt for an original Liberty and go down that route, you have quite a lot of options for the power section.
The original spec replica will take time over a replica that plays the part but on spot on on cosmetically that is a shortcut in construction time plus with both options, modern technology cuts build time by huge amounts. The biggest problem is finding the original drawings or you can spend time taking measurements from the original, back and forth to Bovington, that if they allow you near with a tape measure and they now charge £1 per minute to look inside when i last asked a few weeks ago.
I would love to have a go at a A9 but would need heavy lifting gear during its rebuild and build a shed as everything weighs a bloody ton, even that small bit of plate we saw the other day, that was a beast. Did you find what you was looking for the other day after you left.