So I am interested in buying some older ADCOM Equitment , yes I like the style and looks, very plain.  Any advice on what series / model #'s I should look for? 



Pre amp?

CD player?

Thank you in advance.

I've owned various Adcom items and they were always nice sounding and reliable...I went for the tuner-preamp with a 535 when they first came out, later a balanced preamp (can't remember which one) used with different power amps, and more 535s (used and new, including the 535II) both for studio and otherwise. Sold 'em all eventually except a 5300 that's used for remote (deck) speaker duties...that amp sounds great and was seriously inexpensive used. Nice stuff, but watch for oldness issues...leaking caps, hair loss...
In the past I've used a GFA5802 to drive Martin Logan Ascent ES hybrids. All MosFet heavy bias AB amp. A fair amount of heat but no fans. I had to go to a Pass X350 to upgrade. The Adcom is still on active duty driving a pair of JBL 4430s.

It's a pretty good amp for the money.
I had a GFA 555II for a couple years. Bought it used. I never had tuff speakers to drive,so that thing never broke a sweat. I think I sold it for what I paid for it.
The GFA 535 amp was reputed to be the sweetest sounding of the amplifiers, if you don't need the power of the 555.  I agree with Wolf, you should watch for issues related to age.