Hi Ruben,
There is no problem with putting the +1 on any page on your site people might want to share or 'vouch' for on Google+. If it's easiest to add it to all of your pages, that's fine too. I like removing social buttons from pages that aren't likely to get shared, simply to improve page speed.
No, there is no concern over speed of +1s as long as they are legit. A popular blog post may easily get 100-200 +1s in a day.
It sounds like you already have a G+ community and are trying to build it more. That is a good thing and something Google wants as well. As long as you aren't trying to fake/game anything, go for it.