You are correct about the DLCs, you will keep your progress and can continue where you left off after purchasing the DLC or re-subscribing to ESO+.
After losing ESO+, your materials in the Craft Bag stay there, you can take them out of there, but you will not be able to store any new materials in there
Also, if you have 100 ingots in your character inventory, they will pull the ingots out of the craft bag to blacksmith. So, they will diminish your craft bag stash first.
Materials in the craft bag will stay there but any new ones you get will go into your inventory (and can be stored in the bank or in chests in your home). You can remove them from the craft bag if you want to but the only reason to do that is to trade them with other players. When you craft things it will always pull materials from the craft bag first (then your inventory, then the bank) and there's no way to change that, so over time materials you use will be removed from the craft bag and build up in your inventory, but ones you're not using will just stay in there.
You're right that DLC you only have access to through ESO+ will be locked. You'll keep any progress you've made, including skills you've unlocked and items you've earned but won't be able to make any more progress until you resub or buy the DLC.
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