Zac, pace yourself. The three that you have now, the DN MN and SN, will take you a good deal of time to read and comprehend. There are four large Nikayas: the three above and the AN, the Anguttara, the anthology of which you've mentioned. The anthology is less than a quarter of the whole collection... a complete translation of that collection, also by Bodhi, is hoped to be out in a years time, published by Wisdom. A years time is long enough for you to read most of the three you have, so do that and don't spend more money than you need to for books you aren't going to read anytime soon.
The khuddka is broken up into pieces and you'll have to buy this part and that to get it all. Again, don't fret to much, as the first few books are online at accesstoinsight.org . Search on google for Thanissaro's PDF version of the Ittivutaka. Go to http://www.ancient-buddhist-texts.net/T ... /index.htm
for the Udana. Its pretty good - but has some quirky, and consistent, grammer issues. The meaning comes through alright though. You can order a copy of K.R Norman's "Group of Discourses" from amazon, and that's a translation of the Sutta Nipita. Its good reading.