The section between Warminster and Westbury will be footpath, not used it so can’t comment. From Bratton White Horse onwards you’ll be fine.
To see a good selection of tanks you’ll need to wait til the Imber Range tracks are open which will be 12th and 13th November only for the Remembrance Weekend. Imber Church will be open both days, Service on the Saturday. Always subject to change by the MOD. Tea and coffee will be available.
If you look on your map for the Warminster Training Centre where the metalled road turns to gravel this will take you all the way to Imber. There’s loads of rusting tanks along here, you obviously must stay on the track.
You can exit the Plain at Gore Cross then pick up the Imber Range Perimeter Path but really there’s loads of options.