Questions appear immediately when asked. In fact, it can be some bit of lag before they hit the review queue. I can't answer the how many part definitively or with any citation (there are a LOT of meta questions on review queues). From looking at my First Post review history (as compares to some other review queues), it appears only one reviewer is needed. That may vary depending on reviewers and queue - I see suggested edits in my history that were reviewed by two people and also just me. It may also depend on who is doing the reviewing and their rep level.
I personally don't always (often don't) upvote a question I review, particularly if it's on a subject I'm not familiar with. I look at the question in terms of formatting, tags, provided information, readability, etc. I make any edits, comments, flags, or close votes as applicable, or if there's a clear case for me to vote I will, and then move on. If it's not good, or I don't know if it is, and there's absolutely nothing I can do to improve it, I just hit skip. If it looks like a well-formatted question and I can't improve it, but I don't know the subject matter enough to vote up or down, I just go with no action needed.
The upvotes may or may not be by a reviewer. Yes, some people may just upvote a bad question, but that's regardless of whether they're doing so in a review queue or not. There is some concern about 'robo-reviewing' and poor voting when chasing badges, but in theory the system has checks in place to help prevent that. I too have noticed an increase in low quality questions with upvotes, and I mentioned it in chat and PolyGeo and I had a little back and forth, but the conversation didn't really seem to take off.
In your specific example I'd have voted close unclear, but likely wouldn't vote up or down on the question for a couple of reasons. First, it appears to me language is something of a barrier and I try to give broad latitude with that. Second, since we don't get notified when questions we've voted on change, I hate to downvote something that could be fixed and me miss coming back to reverse or remove my vote. I tend to only vote on a question when it's clear and I can determine that yes, it's good and useful, or no, it shows no effort/doesn't belong/whatever and that there's pretty much no amount of editing short of replacing the question entirely that would be likely to change my mind.