I just did mine a month ago on a W201 engine. My manual stated that to drain the t-converter, you need to line up the drain screw with the small hole in the converter cover. This is possible with 2 guys and a car lift, but not if you are doing it with ramps or stands. I did not do it, and instead pulled off the pan and removed the filler/dipstick. After letting the car sit and drain, I noticed the fluid gurgle and a bit more came out. Maybe the converter released it? Anyway, I don't think you will ever get all of the fluid out without pressure. You will notice the book gives a flush fluid amount and a simple replacement amount. Flush gives a bigger replacement amount.
I would suggest not worrying about the converter and put new fluid and filter in. If you have a fluid extractor (Griot's Garage in the US has them online) you can easily pull out a few qts/ltrs from the filler later and add some fresh fluid. You may want to do this after a month or so of driving....give you the peace of mind that the tranny has very clean fluids.
As far as the drain bolt. You could either leave it in and start using a fluid extractor (thus never needing the pan bolt) or work on getting it out before you decide to put the pan back on. Maybe take the pan to a shop and have it tapped or drilled out?