The fallen in the datasheet are Chaos Space Marine Chosen
This is good and bad. The good news is, they can kick ass and take 5 special weapons (plasma, melta or flamers mainly - though there is a 5 point power fist cheese option I wouldn't recommend in a friendly) on top of infiltrate. The bad news is, you don't have that many models. How friendly is your friend with what-you-see-is-what-you-get? They are all essentially veterans (2 attacks, higher leadership base) - but in the data slate have
CSM-flavored upgrades.
Can we link blood of kittens here?
http://bloodofkittens.com/blog/2014/01/25/bok-reviews-dataslate-cypher-lord-fallen/
A unit of Chosen / Fallen starts at 90 for 5 models, can add 5 more (another 90) and take up to 5 special weapons - plus the Chosen Champion gets a pick or two on the specials chart. 10 chosen (180) + 5 meltaguns (50) would be 230 ... and you can keep adding. You could hit 1000 on 3 units...