Pokey, the quickest way back to Firelink from the Depths is pretty much the long way you came: back to the lower Burg, then the shortcut through the aqua duct with the undead merchant.

You can only proceed to Blighttown from the Depths once you've defeated the area boss of the Depths, unless you have a master key. If you took it as your starting gift you could go to Blighttown immediately; if not, you can still take an alternate route which is granted by the master key. After you beat the boss of the Depths that merchant who was down there, I think Domnhall of Zena was his name, he relocates, for some insane reason, to the part of the bridge near Firelink that you have to jump to.

Anyway, if you have the master key you can go down to the New Londo Ruins, take an immediate right into another cylindrical construct, similar from the one which you just emerged, and the master key opens a gate to the Valley of Drakes. You cross a rickety little wooden bridge and then proceed into the large tunnel for the shortcut to Blighttown. Whether you want to use this shortcut depends on how you're playing the game. If you're trying to collect as many items as possible and light all bonfires, etc. then you'd probably rather go the normal way in, via the Depths. If, however, you'd like to avoid as much of Blighttown as possible use this shortcut. You'll fight 3 very large enemies off the bat, who may take a few attempts to master, but after them there will be a few poisonous mosquitoes and the rest you can avoid if you're careful. Hint: The boss' lair is located in a tunnel on the part of the area that looks like a beehive with something like round black spikes coming out of it (maybe they have a proper name?)

I tried-- rather sheepishly-- my hand at the Asylum demon half a dozen times. Every time he crushed or beat me to smithereens. I decided to avoid him and just revisit the rest of the asylum. The Rusted Iron Ring would be an invaluable item to have in Blighttown.

Synonamess Botch said
Guys I have seriously hit a wall.

Sounds like you're in the same spot I was the other week before I joined arms with xtal, though admittedly in that post I only seemed to articulate my situation with the sentence "I’m struggling on where to go next because it seems that everywhere is hurting me badly at the moment." Oh! Just found it:

geggis said

Steerpike said

...from a quest/story/progress perspective, your next stop should be the Depths.

I recommend this as well, especially now you've defeated the Capra Demon. I was pretty much in the same position as Steerpike towards the end of the weekend: everywhere was kicking my arse and I didn't know where to start chipping away at next. After me and xtal took the Capra Demon down I was pleased to see that the Depths felt do-able so my next port of call is there. It's tough behind the Artorias door (but close to a bonfire) and scary down in Darkroot Basin.

Incidentally, I too lost a lot of souls and humanity in the Darkroot forest area, presumably you mean behind the Artorias door? Those ghostly Darkwraiths are tough (if you don't glitch kill them!). Botch, there's also a bonfire directly to the left of the Artorias door behind a secret wall.

I've been mauled by surprise a few times now in Sen's Fortress. First by misjudging a swinging blade, next by a mimic, then when I finally emerged onto the rooftops I was met with a giant firebomb exploding in my face.

That place is damn tricky.

Botch, try restoring your humanity and look for a certain summon sign under the stairs leading to the Moonlight Butterfly. It may be very helpful.