Hi Jim,
I'm new to Churchills and like Shermans there were many versions and variations.
Without a doubt the best Churchills on the market are those from Gordon at Cromwell Models. I don't have much experience with resin builds having only done the AA Tilly but I'm working my way up to one of his Bobbins lol, lol.
On the kit side, the Legends conversion kit is being re-worked and currently unavailable at least here in the UK. I believe it only contains the turret parts but the re-worked version may have the necessary body parts too, but I really don't know.
I used two Resicast kits for this one. The AVRE Turret which comes with the necessary parts for the body and the deep wading set. Both I believe were made for a Dieppe Churchill and so the bin is incorrect at the back as it needs the sloping sides, something Gordon pointed out to me and something I've got to change and the exhausts are different on the D Day tanks. Also for a Churchill deep wader on D Day they carried the extra boggies on the rear. These are not available and were a kind donation from Ian at Friendship Models.
My advice would be to decide what sort of AVRE you want to build and then take it from there. Both the basic AVRE as I have and the Facine are do-able from the Tamiya Mk VII. The Resicast kit comes with a complete new front section so some major surgery is required as is a little on the sides but if I can do it most anyone can. If you want to do a Dieppe version then the Resicast kit is fine.
Problems only arise if you want a D Day vehicle with wading gear as they were the vehicles that had the boggies on the back and the different extended exhaust, and they aren't available as a AM product that I know off, which is why I own Gordon and Ian a big thank you.
That said if you want to do one shortly after landing then neither of these two things become an issue as the boggies were removed very soon after landing for whatever reason, perhaps they simply got in the way.
Have a lookat IMA stuff on Ian's site at Friendship Models. They have the bridge layer as a full or two part conversion, something I might try and do later in the year.
A Facine should be do-able on the kits I've used as you would only have to build the wooden support at the front and make the sticks from a brush or something similar. A lot of bundles to tie thought lol, lol.
Re the tracks I used the Tamiya ones as thsese would seem to be right for the kit I'm building. There are resin sets available if you need the earlier ones.
I'm not quite ready for a full resin tank yet but but by the time I do the AA Mobile canteen and another one of these I hope to be.
As I'm reading Mr Churchills Tanks at the moment the earlier gun tanks are looking very interesting and if I go down that road then Cromwell Models is the way to go.
if you have the cash and experience/confidence with resin then get one of Gordons excellent Churchills form Cromwells Models. They may well work out cheaper than getting all the parts you need and going through all the pain lol, lol.
Hope this helps a bit, I'm sure there are other more qualified than I to say.
Cheers
Al