I have an original 645, which does not differ much from the 1000S, 80mm 2.8 (both N & C lenses), 150 F4, and 210 F4. I also have a 645E body.
Have no complaints at all about any of the kit, it all works really well and the lenses are all superb. Have been looking around for a 35/45 cheap on the second hand market but they are fairly scarce at the price point I'm hoping to pay. I may have to lift my price...
In some ways I enjoy the older 645 over the 645E. More solid feel, quieter mirror noise that the 645E, and as Nige said the dual shutter buttons come in really handy. And I can use the ground glass on the 645. Note that if you get a prism with the unit, it's a common fault to have a horizontal line across the finder that looks like a scratch. Apparently it's separation of glass/mirror elements inside the finder. Mine has the line but now I'm used to it I never notice it any more.
I also graduated from a TLR to the Mam645 system and I enjoy both cameras immensely for different shooting situations.