The 1.5 used in the 1st gen CRXs was a 1.5 EW1 (I have a 1.5 EM1 in my 81 wagon) though they are essentially the same engine. Very easy to work on, very durable, very reliable and very cheap to fix...BUT, they do like to blow headgaskets (check your fluids and for smoke) and the carburetors are a mess. A good Weber carburetor makes for a good replacement when the factory carb starts acting up (or if it already is) Replace the timing belt, tensioner and water-pump ASAP if you buy the car. Thats about it.

As for generations,
The CRX was first introduced in 1984 when the Civic was redesigned into it's 4th generation. Base models had a 1.3 (EN1, I believe) with about 70-ish hp.
The 1.5 EW1 was optional with 76 hp.

The Si came out in 1985, and had a fuel injected 1.5 with 91 hp. The 'HF' replaced the 1300 CRX and came with a 1.5 (carb) EW1 standard.

CRX was redesigned in 1988 for its second generation. HF models were powered by either a new fuel injected 1.3 or 1.5, and the Si got a completely new, fuel injected D16 engine.

1991 was the last model year for the CRX.