Peachy I see this, since I just beat Dark Souls for the first time last night (haven't played DeS, DS2, and Bloodborne, but I intend to). I'll make some comments on it.
Friendliness: Not sure about the others, but Dark Souls is fairly newbie unfriendly at the start. A lot of useful mechanics go unexplained without some digging. Yahtzee said there's a wall in his review, and that's spot-on. Once you break through said wall (amount of time depends on you), the difficulty is pretty manageable. I got through Dark Souls on fairly amicable terms without having to stitch a guide to my face (I only referenced one when I really needed it for navigation and hidden bonfires, but went blind for bosses and new areas). I hear DS2 is a bit more newbie friendly, but I also hear the story isn't as strong and most of the bosses are "dudes in armour" (compared to DS's...4? Apparently one of them is even shoe-horned into DS2).
PC: The PC version of Dark Souls isn't great, but there's patches and mods available that at least allow it to fuction (I strongly recommend using a controller as well). It's worst at Blighttown, which is known to dip to around 15 fps across all platforms (though that's hardly the limit of issues Shitetown has). DS2 is supposed to be better optimized for PC. PTDE also comes with the Artorias of the Abyss DLC for free (to avoid spoilers, it contains new 4 bosses, several new areas, and further clarification on one of the more interesting stories in the game. Maybe 4-ish hours of gameplay).
Price: Dark Souls is pretty commonly on Steam sale for $5 USD. I mean, I bought it on a whim last year and I've spent about 90 hours so far just derping around. Sweet deal. Regarding DS2, it seems like the vanilla version is unavailable on Steam and you're forced to buy the more expensive Scholar of the First Sin remake (which was released a few months ago, so don't expect it to have a deep sale). Used copies of DeS I've seen dirt cheap lying around Gamestops.
I say starting with Dark Souls 1 is fine, however since I don't have a proper reference for the other games, interpret that as "don't worry about it, you'll make it through eventually" than a recommendation from a knowledgeable comparison. At the very least I enjoyed Dark Souls more than I thought I would (despite the wall and how the game is a bit rough on the frame rate and hit detection), and I'm excited to play the other games.