Well, thanks to AkariK, I was able to get my platinum tonight!
First, we met around the Iron Golem so he could lend me the last weapons I needed. We had some trouble with invasions and such but eventually got it done. The problem was that he apparently didn't get back his Cursed Greatsword of Astorias from a previous person. So I didn't get the trophy and we weren't sure why at first. I thought I had all the farmable and purchasable weapons. But we finally figured out he had 2 regular Greatswords (and I had that already). I did not know that you just had to hold them once - I thought I read that you had to have them all at the same time. Apparently not!
So first we took care of the Iron Golem. AkariK commented on how much harder it was than he though it would be because of the pyro nerfing. We had Tarkus there too so it wasn't too much trouble, but it just took a lot of fireball beatings to take him down. I think I used all 8 of my Fireballs and all 4 of my Chaos Fireballs and that was in addition to whatever AkariK and Tarkus did! I then travelled to Anor Londo and breathed a sigh of relief when the trophy for Anor Londo popped (as it glitched on me in my original game).
So then AkariK helped me beat Sif which was a challenge because of course as soon as you enter the forest in human form you get pounced on by Forest Covenant defenders. There were a lot of people to summon which actually made it hard because I couldn't find his sign for a long time. Eventually I just decided to join the covenant which cut down on the invasions, though I still had a couple regular invasions while I was searching for his sign. Finally, we got another summon and beat down Sif. One thing is for certain - the game is definitely very vibrant online. Even at our levels (120 or so) there was a lot of activity on both the invader and helper side. And this was 1-2 AM Pacific on a Wednesday night.
Anyway, then it was back to Anor Londo to get to the blacksmith. Once again, invasion city... Finally we made it to the great hall and a pretty tough invader came in. While AkariK fought him I went to the blacksmith and quickly made the Cursed Greatsword of Astorias - got the weapon trophy followed by the platinum! In the mean time AkariK got killed and the phantom showed up right in front of me at the blacksmith while I was text chatting with AkariK. I'll give him credit, though, in that he seemed to realize I was doing something and he waited for me to move before engaging. I held him off for a bit but the lag eventually caught up to me and he got a few backstabs in (or lagstab as AkariK called it

).
Anyway, we met up again so that I could give AkariK my Cursed Greatsword so he can continue to help out others. I can't really do the same since I'm missing all the other second boss soul weapons. Just in case I want to return to the game I backed up my save to PS+ cloud before giving him that. And since I did that, I also unloaded all my slabs and titanite chunks on him

. I'll just restore it in a day.
In any case, it was nice to get the platinum with only 1 1/2 playthroughs. I really was enjoying the second playthrough, though, and wouldn't have minded finishing it off. But on the other hand, I was done with the early parts and now I was about to head back to stuff I did not that long ago so it would have been less interesting. It was definitely fun going through the early parts knowing where everything was and pretty much owning the game

.
With the time I saved from finishing off this platinum, I pledge to go back to Demon's Souls and finish that up. But first I think I'll take a break and play either Skyrim or FF XIII-2 next...