I Want To Start Collecting Bills...

I think for $1 bills, you should first try and get all the Federal Reserve Banks together, as you said for the current 2006 series. Then, you can move onto different series with pretty much the same thing (getting FRBs). As for the weird numbers and star notes, I just put them aside because for the series/FRB combination, I want new notes.

And that's the other thing, as in coins, you want the highest grade you can possibly get.

There are 12 FRBs, and that's why you see the letters A, B, C...L on the serial and in the seal. And since the creation of the FRB, there's been quite a lot of series, and those can get quite expensive. As of now, there are 2006, 2003A, 2003, 2001, 1999, 1995, 1993, 1990, 1988A, 1988 for $1s. The colored and big-head versions have different series years.

And the little A means a change in signatures or printing styles, but still in the same year of change.

That's all the information I can give you as of now. I personally just collect one style of every design change (so 3, the small heads, the large heads and the colored heads) of every denomination. I guess it's up to you on how you want to collect them.

If you are going through bills that you get from the bank there are a few things you should keep your eyes open for. Some of these are rare, and command a decent premium:
As far as serial numbers go:
replacement notes - there is a star in place of the trailing letter - A16834837*
Binary - the serial numbers only have two different digits (e.g. 85588855)
Radar or Pandendrom - the number is the same forward and backward -12599521
Low numbers - most people consider 5 leading zeros very low - 00000521.
High numbers - On modern series the highest number is 96000000.
Solids - all the same 55555555
Almost solids - usually 6 or more of a kind 55565755
ladders - numbers progressivly go up or down - 23456789

Obviously any errors - too much ink, missing ink, cutting errors - the edge fo the bill is cut off, gutter folds (the paper had a fold in it when it was printed and the creased part didn't get printed on.)

Since you have many questions and just a very general knowledge of currency, you will probably want to pick up a book or two.

just a question please, which numbered bill would be most sought after?, and which the least?, on the list of special serial numbers posted by karrlot and quoted by manilagalleontrade. thanks!

The 00000000 serial numbers are almost always specimens so they are the most expensive, then comes the other solid numbers (lucky numbers are more expensive e.i. 77777777, 88888888) then the ladder (especialy 01234567)and then the starnotes (especially low numbers).

I already collect and trade CU blocks, if I worked at a bank I would be taking advantage of the access to CU straps. You could collect all of the fancy notes mentioned by others and also work on CU district and block sets. Collecting a CU block may seem a bit anal but it is also extremely addictive like any other type of collecting and its fun when you make progress. Also it fun to make new trading friends online.
Frank