Guys I need some help

I currently have 3 Beocom 2's (MKI) connected to the older style PTSN base on the ground floor of the house. Everything works fine.

Now I want to add some 6000 to 3 of the bedrooms on the first floor making a total of 6 handsets. I know thats possible but I'm concerned as I plan to pick up the 6000 via ebay or other sources as to which versions/models of the 6000 are compatiable with my system.

Also am I right in thinking there is a base for the 6000 which can handle 8 handsets. If so can I link my MKI beocom 2's to this instead of the current PTSN base ? Would it be compatable. You see where I'm going here that would give me all 4 bedrooms on the first floor covered.

I have read the FAQ and think I'm okay but I'm still not sure, and want to confirm before blowing a few hundred on an incompatable system.

Yes I know I could add another 3 Beocom 2's but in my view the 6000 is better phone to use and where they are not 'on display' quite as much make a better chioce (the 2 is just so stylish but that dam keypad !!!). I can also pick them up a whole lot cheaper than the 2's

Finally what about the Beocom 1 is that an option as I gather that a 6000 in disguise !! 

Thanks in advance