The numbers on the gates are the level of shadow power you need to open em. As always walkthroughs are on gamefaqs. I really can't guide you through this way, the game is just too big. If you can't continue further into the game it means that you haven't found all the dark souls in the unlocked part yet of the game. Also if you only have the asson, you're still very early in the game. Also don't forget you can shoot certain doors in liveside to open them, and look for snamm ledges, you often need to scale a wall to get to another part of the game.
You basically need to get to the Asylum from the Marrow Gates (snake), from there the game wil sorta open up by giving you multiple paths to follow. The 3 temples at the bottom of the map will give you key powers without which you cannot finish the game (climb bloodfalls, walk on fire/lava and swim in boiling water/lava).
The game will seem a bit confusing at first, but that's only because of its sheer size, but it is build very logically: a certain ammount of dark souls will let you open the next gate where you will find a few items to open other parts of the game, allowing you to collect more dark souls, to open more gates, and so on...
Also not a single "level" can be completed right from the start, there's a lot of backtracking involved in this game.
The question about the asson: you prolly saved while holding it, just go to the items menu and unequip it.
About the old save: better to start over if it has been too long, if you pick up the game after a few months and it is half unlocked,,you could spend ages looking for what to do next. Starting anew might be easier imo