Disclaimer: I can't answer for Nikon, or any system other than Canon. But I can attempt to answer some of your questions in general, as relates to Canon film cameras. This will also serve to answer the same question someone else may have, but from a Canon point of view.

Canon hasn't released a new film SLR since the EOS 30V and EOS 300X in 2004. The last professional model was the EOS 1V in 2000.

• The clue is in the name EOS - all EOS cameras support autofocus with all Canon EF lenses.
• The later cameras support Canon's ETTL flash system, and in the case of the 300X at least, it supports the latest ETTL-II flash system (which improves on the original ETTL system by incorporating focus distance information).
• The metering and autofocus systems have naturally evolved over time. But considering the EOS 1V has 45 autofocus points and can use f/8 lenses, I think it's quite good for the time. There are also other features that didn't make it into digital cameras, like eye-control focus on the EOS 3. Even the lowly 300X has 7 autofocus points.

As I mentioned, Canon hasn't released a new film SLR in a decade. You could still pick one up from ebay or similar. If you want to start small, light, and cheap, you can pick up for example a 3000V for a week's worth of Starbucks. A 1V is considerably more expensive; it's also built like a tank as it was the professional workhorse of its time.

In my personal experience, I have a 300X I bought new in 2005, and which I've successfully used for years. It works with all the latest Canon lenses that I own, it even works with the off-camera flash system I bought. The autofocus is sufficiently accurate, if not blisteringly quick. I use Ilford XP2 film that can be developed using the same chemical process as colour film, but there are several options for the home darkroom. I wouldn't use it for action photography, but it works well for studio and street photography.

As relates to Nikon, I believe you can still get an F6 - arguably Nikon's best film SLR - quite easily.

Other big competitors in the latter years of film SLRs were Pentax and Minolta. You can easily pick up a system for not much cash. Each has lenses that work on modern digital cameras (in the case of Minolta, the Sony SLT range).