I'd suggest that since you agree with some parts but disagree with others, you assign probability a lot less than 90% to the whole hypothesis. So you should think I'm irrationally overconfident in the whole lot, and upvote please!
If you want some detail, I start from the "Great Filter" argument (see http://hanson.gmu.edu/greatfilter.html). I find it very hard to believe that there is a super-strong future filter ahead of us (such that we have < 1 in a million or < 1 in a billion chance of passing it and then expanding into space). But a relatively weak filter implies that rather few civilizations can have got to our stage of development - there can't have been millions or billions of them, or some would have got past the filter and expanded, and we would not expect to see the world as we do in fact see it. The argument to the universe being finite (and not too big) then follows from there being a limited number of civilizations. SIA and MWI must also be wrong, because they each imply a very large or infinite number of civilizations.
Your conclusion doesn't follow from your premises. The lack of a strong filter implies that a not insignificant proportion of civilizations colonize space. This is consistent with there being a large universe containing many intergalactic civilizations we will never observe because of the expansion of the universe.
The 'Irrationality Game' posts in discussion came before my time here, but I had a very good time reading the bits written in the comments section. I also had a number of thoughts I would've liked to post and get feedback on, but I knew that being buried in such old threads not much would come of it. So I asked around and feedback from people has suggested that they would be open to a reboot!
I hereby again quote the original rules:
I would suggest placing *related* propositions in the same comment, but wildly different ones might deserve separate comments for keeping threads separate.
Make sure you put "Irrationality Game" as the first two words of a post containing a proposition to be voted upon in the game's format.
Here we go!
EDIT: It was pointed out in the meta-thread below that this could be done with polls rather than karma so as to discourage playing-to-win and getting around the hiding of downvoted comments. If anyone resurrects this game in the future, please do so under that system If you wish to test a poll format in this thread feel free to do so, but continue voting as normal for those that are not in poll format.