There is an overview on fandom.com of places where you can find Void Salts:
Looted from Storm Atronachs.
Can be very rarely looted from Falmer.
Can be bought from alchemist's shops.
Proudspire Manor alchemy lab in Solitude.
Honeyside alchemy lab in Riften.
Hjerim alchemy lab in Windhelm.
Arch-Mage's Quarters in the College of Winterhold.
Sounds like a bug involving trespass checks- perhaps it's registering you as having broken in when you enter buildings. I'd try saving, then allowing yourself to get caught actually trespassing, and see if that clears it.
Potions won't fail regardless of alchemy level if you use the correct ingredients. According to the wiki, there are 4 ingredients you can use for fortify smithing:
Sabre Cat Tooth
A common method of leveling smiting is to buy as much iron as possible, make iron daggers, and enchant them. Sell the enchanted daggers ...
You are correct. Skjor should stay dead after finishing the Companions quest, The Silver Hand. However, according to the UESP wiki, there are bugs associated with Skjor:
Sometimes Skjor will reappear in Jorrvaskr, alive or dead, after he
dies during the events of The Silver Hand. He may also reappear in
Jorrvaskr and still give out quests....
I'm assuming you are asking if you can fly to Solstheim, the main area in the Dragonborn DLC. If that is the case, then that is not possible.
As travel in any one direction is not possible, dragons cannot be used in place of a traditional mount, such as a horse. It is possible to fast travel while mounted on a dragon, however travel between Skyrim and ...
Magic effects can be found in the "Object Window" of the Creation Kit in WorldObjects → Static → Magic:
From the list on the right, quite a few effects can be chosen, ranging from the small
icons you see in the in-game Magic menu (on the right in the picture below), to larger animated effects (to the left on the ground and in the back):
As the category ...
It's not entirely clear from your description at which point in Dawnguard's main story you are, however it sounds like you're either banished from the castle or not welcome yet.
In either case, my suggestion would be to try to push on in the main story for a bit. Helping the Volkihar clan should pretty quickly give you the reputation to roam the castle ...
There are a few options on how to survive an overly difficult fight, but the most basic one would be to run away and live to fight another day. There are few situations where you are forced to fight dragons, and for those rare occasions the quest will provide you a strong companion, the rest of your time you can flee. Run a far enough distance away and fast ...