I'm about 70 hours into my first playthrough, and I have yet to enter the Vegas Strip. As I understand it, the game has different outcomes, depending on how I align with different factions. The first part of my question is, how many different outcome threads are there (I'm assuming they are the ones tied to each major faction)?

Second, while my current character has high speech, I'm considering trying a melee/unarmed brute in hardcoe/Very Hard. If I do this, and don't add points to speech, will it impact on my ability to choose which faction to align with on a second play? Or will this be dictated solely by my actions?

There are four major threads. But they can interweave a bit. Speech does not block you off from any major faction threads.