I've noticed that in playing a PC who doesn't speak, while I can use a variety of emotes to describe what my PC is doing, it does limit my actions alot. This is fun, and a challenge. The few quests I have been able to do, have been "OOCly talk to this placeable" Or have another PC talk to the giver NPC for the quest.

This is great, and lets me include people by trying to tell them what I want so they can convey it to the NPC. The only real problem with this is: When everyone else is off questing, or otherwise busy. My actions are limited in that I cannot talk to the NPC merchants, I cannot ask them for quests, etc. This PC depends a lot on other player interaction for that sort of thing.

So my question was, when there is no PCs around to help me, is it all right to initiate an OOC conversation with an NPC, emoting my responses to their words as I go through each option, as a 'reply' treating the spoken reply, as OOC?

There are situations in which, in order for the player to maintain continuity (which is also entirely the player's decision), they should not speak to NPCs, but for "OOC" conversations (i.e. opening merchants, quests, etc.) I see no reason why they shouldn't be able to.