Sounds like a good concept.
Here is what I would do. Plan out an army now before buying any more models. You don't have to work out all the niggly points costs just broad ones, ie I want to spend ~150 on a predator and have two decent troops choices, probably 300 points each.
Don't go for a certain points limit, just what you like the look of and what you think will make a good combined force of arms.
Heres the rub: Thousand sons are great at shooting, but always poor in combat with just about everything except lone characters. Infiltrating Chosen (representing Alpha Legion) can be tricked out for almost anything, so making them able to hold their own in close combat and using infiltrate as an attention grabber will help your Thousand sons.
Berserkers and Bikes are okay in support. Berserkers are like the complete opposite of Thousand sons, shooting is poor, and they'll clean up most things in combat except perhaps some uber characters. So running them side by side isn't a bad idea at all. And always give them Rhinos.
Bikes are neither here nor there, they can fit into most lists.