When you clean teak, always scrub ACROSS the grain. If you scrub with the grain, it will dig out the softer wood bands, and cause the harder rings to appear lifted.
You can probably get by cleaning and sanding the hand rails, but if your hatch sliders are cracked as you say, you're probably better off replacing them. You also say you have a wood shop, so you may find that you're better off just buying some teak boards and cutting yourself, rather than buying pre-made pieces from someone else. Or maybe not... From your picture, it looks as if the hatch sliders are L shaped in profile, which would be pretty easy to do with a router table. Mine were U shaped, so that the hatch lip slides on the U channel, and there are other bevels and stuff. Probably not to difficult to do with a router table, either, but I was able to buy replacements for my boat, and they weren't terribly expensive... Maybe Hunter has parts for you?
Finishing them is up to you. Some people like silvered teak. Others like brightwork. Know that varnish will require 8-10 coats to start, and 1-2 coats each season, and probably wooding down and starting over again in about 10 years.
Some use Cetol, which is really like a translucent paint that still allows some grain to show through. My understanding of Cetol is that it will darken over time, and after a few years with a few maintenance coats, you'll want to get it off, and it's a royal PITA to remove. If you go with Cetol, be very careful of the color - the Natural Light color does have a pronounced orange hue. It's impossible to really know which color you want... I would not use Natural Light again due to the orange, though the wood does look ok on my boat. (I'm a big fan of amber colored plain varnish on mahogany...)
If you chose to go with oil, pretty much don't bother with any teak oil, such as Watco Teak Oil available at a big box store - it will wear off very quickly. An acquaintance in FL has been using Semco on his teak, and he's been very happy with the results and longevity.
Finally, there's stuff called Honey Teak. I've had no experience with it, but I believe it's an epoxy type of finish for teak. There are testimonials that swear by it, but I believe it's somewhat expensive.
Brian