I've never had any issues with emulating an N64. Goldeneye works perfectly. And also due to how N64 games are coded the emulated versions can be run in much higher resolutions without the horrible full screen anti aliasing of a real N64.
However I also still prefer to play the games on the real N64, as most people do for most systems. For this I have a CD64 (similar to the Doctor64 but a different make) and a Mr Backup which is my preferred one. It uses Zip disks and so you can write the save games directly to disk as you are playing, along with the ability to save other things to disk such as the config settings for each game, and the ability to alter the roms.
Back to the questions about the Doctor 64. I've not seen the ram expansion unit for it for sale anywhere in a long time. This is as already mentioned due to Nintendo's enforcement of restrictions on backup units a few years ago, which scared ebay into banning the sale of all such units and related items. However they do appear sometimes and if you can grab them on a buy it now before ebay spot the sale you are usually ok.
I noticed you were also looking for a DS-1 SRAM cartridge. I have one that I don't use any more so would be happy to sell it to you for a reasonable price. Make me an offer if you are interested.