Some good ideas there buddy.
My 2cents on them:
-Yes supply should be lockable by the guild that claims the castle, because right now you have to have a guild member guarding all the supply pick up points yelling “DONT YOU DARE TOUCH THAT SUPPLY” and still players pick up the supply.. Maybe if the castle was under attack it would be automatically unlocked since there might not always be someone around to unlock it. Or if the supply limit has been full for 10-15minutes.
-Yes the upgrades should definitely cost something else than gold, right now there are so so so many money dumps in the game that this is just stupid, also with the frequency of capping castles and loosing upgrades, playing 1g for an upgrade is absurd, also makes the rich guilds even more powerful. They should cost Badges of Honor and supply or just think of some other currency for the upgrades.
-I don’t really like the arrow cart on wheels, would lead to some exploiting for sure, ppl driving their carts to impossible locations.. Some areas do need fixing though, I hate how for example mesmer can get his/hers illusion up to the “trebuchet-spot” in greenbriar from the ground level.
Other ideas seem fine too.