I don't know if this is the appropriate section to ask for quest help, so please forgive me in advance.

I appear to be completely stuck in the Dragonborn content.

I have done all of the main quests that I know of, the only two quests I have in my quest log are: Summit of Apocrypha and New Source of Stalhrim.

I cannot complete New Source (I have the map and need to talk to Baldor) because Baldor won't talk to me.

In the Summit quest I need to unlock the "Bend Will" shout. I already know it (I've done the stone cleansing quest) but apparently I only know 1st word out of the 3. I've completed all Apocrypha books that I know of and learned various Apocrypha-related perks (the ones where you get a choice of 1 out of 3) like Black Market etc. I looked it up and the 2nd word is learned from The Patch of Knowledge and 3rd from The Gardener of Men. I have both of those quests completed.

Storn is long dead in my game and I have killed Krosulhah too. I also have a Misc. quest to find the Black Book in Tower Tel Mithryn, the quest from encountering a wandering madman. However, I've retrieved and explored that book long before I received the Misc. quest, right after I got the key to the special little room from Neloth.

So..what do I do now?

So if I read this correctly you are trying to get the 2 other words for the bend will shout? Okay well you actually get it by following the main quest line. You have to complete the black book that neloth gives to you. You help him in the dwemer ruin, and then the black book that you receive the two other words is right underneath you after you help neloth. That black book can be quite a challenge but at the end the daedric prince of knowledge and the unknown will give you the 2 words you need. The summit of apocrypha is actually the black book you find in the dwemer ruin. It's where you kill miraak. You need to complete that quest In order to receive the 2 words of the shout.