Hey - if you pledge at a tier, you get access to all posts of that tier (and less) both past and future, so long as you don't lower or cancel that pledge. We do 4 paid updates a month, and the way Patreon handles those is it bundles them together as a single charge at the start of the next month. You can also choose a monthly cap on support if you have a particular amount in mind, which we take into consideration for some of our rewards but doesn't affect any of Patreon's features.
tl;dr if you pledge at Bunny tier, you'll get weekly updates, and can set a maximum. :D