The web version on itch is just a demo, but the version you download is the full current version of the game (you need patreon to unlock everything). Once the game is finished there wont be any distinction between the itch, steam and patreon versions. Check the walkthrough to see which quests are public and which are patreon only.
You will be able to play Avarice and Gold & Sand in any order. Personally I would probably play Avarice first, but they don't spoil each-other.