I would order 5 feet for the grille. If the material is cut square when they are preparing your order, you might be able to get by with 4 feet but it is not worth taking the chance.
The amount that you need for the cabinet depends on how it is covered. There are typically two approaches to covering these cabinets. Ampeg currently uses one piece to wrap around the front top, top, back, bottom, and then front bottom. Then they apply a piece on each side. The seams are butt joined to provide a cleaner look.
Alternatively you can wrap one piece around from bottom, side, top, side, and bottom and then have another piece for the back. I prefer this approach because I think that it looks cleaner. You will never see any peeling or separation of the seams from the sides. The originals really suffered from this problem. But then again, when they build these cabinets, they never would have expected them to be still in service over 40 years later.
Other approaches use more pieces of vinyl to save on the overall cost. Whether or not you butt join the seams or overlap like on the original, the amount of vinyl needed is the same. If you are only covering one cabinet, the cost of an extra vinyl shouldn't be a concern. Look at some cabinets and pick an approach that you like.
Duratex has a bumpy texture that can mimic vinyl but it really is something else. Vinyl has lines in it that you can't easily reproduce with a spray and texturing. I would use it on a modern cabinet but not on a classic like a straight back.
Each handle is held in place with a bolt on each side. To remove the handles, you need to unscrew the bolt from inside the cabinet. The handle then pulls out. It can then be easily disassembled for cleaning and restoration. Sometimes the handle covers can be in rough shape. The ones that I've worked on have been solid stainless steel. They were not plated. This means that you can carefully sand them to remove the rust and pitting. With progressive grades of sandpaper and a final buffing, the end caps will look like new.
It is a lot more work than buying modern replacements, which won't look exactly the same. If you want to keep the original parts it can be done. Antique Electronics sells a handle and parts made by Marshall. The end caps are close to what Ampeg used and the parts can be adapted for use.
It really depends on how far you want to take these sort of things to keep it all original or modify the cab to suit your personal taste.
. I picked up the crud cutter stuff. If that doesn't cut it, I'll get some acetone and give it a go with your method. Thanks.
lol 
