yes, print comics, and digital releases of print comics are weekly. new releases sold on Wednesdays.
(most individual titles are of course on a monthly schedule.)
Google for local comic shops if you want to buy that way. You can either just walk in and pick off the racks, or most shops will set up "boxs" to set aside/pre-order the comics you want. This is highly preferable for them. Usually will give you a discount if you do this. since, if they have 20 people ordering Greenarrow, as you say, they can order 20 copies specifically, instead of ordering a random amount, and not having them sell.
And yeah like lanx said, when I was still going to brick and mortar, I would only visit once a month, and just get all 4 weeks of comics at once.
or, you can order from online stores.
Best Comic Book Store Online - Things From Another World
Or, you can buy digital outright.
Digital Comics - Comics by comiXology
Of note for comixology, I would ask you to do your shopping from the online store, and NOT from a mobile platform.
Or, pirate.
(then buy the collected/GN at a later date.)
Why buy from online store, and not mobile platform? more money to the creators. And its easier for you as well. when purchasing, via apple/android/win8 there is a 30% platform fee.
If you buy directly from the website, there is no platform fee.
Also, the format for YOU is more ideal. you can add things to a shopping cart, and buy all at once.
While, purchasing from mobile, is one at a time.
I am not entirely sure how CC fees apply. I would expect buy all at once, to be cheaper then 10 2.99 purchases as well..