How Do You Collect Paper Currency?

I'm currently working on a type set by trying to obtain one note of each series in each denomination and each type of note (Gold, silver, legal tender etc). Of course this can never be completed unless you have DEEP pockets, but if you set your goal to what you know you can get, then it becomes possible. I'm currently working on series 1880 and already have several notes from that series. I'm also trying to complete my large size $1 type set and I'm only a couple notes from having it complete.

When I'm not working on my type set I like to dive into early small size notes (federal reserve notes, USN, silver certificates). Mainly early star notes, mules, and district rarities. Mules especially can be fun to cherrypick because a lot of people just overlook them and certain ones can be quite rare and valuable.

AND FINALLY, when I'm not doing the two above, I collect errors and other odds and ends that 'speak' to me, therefore I have to buy it even if it doesn't fit into what I listed above.

I started out just hoarding any "old" currency I could find (blue seal silver certificates, red seal legal tender notes, etc.) Eventually, though, I decided to try and collect some sort of "Type Set" of 20th century U.S. Currency. My collection currently includes a few slightly older notes from the 1890s, but I can't really afford anything earlier than that. I also decided to only collect up to $100 bills, for the same reason. I'm still missing a few key notes (such as the Series 1896 $5 Silver Certificate ("Educational") and the Series 1923 $5 Legal Tender Note ("Pokerchip"), and there are some "types" I've opted to ignore entirely for now (such as early National Currency Bank Notes), but I've managed to have a lot of fun with it as long as I don't obsess about actually owning an example of every type possible.

Here's what I have so far:

My U.S. Currency Collection

@barryg, I can't believe I hadn't looked at your site before now. That's so very cool. Great work!!