Using FPS override in ML is a very good way to get your shot in focus. Set to around 1-2fps and optimize for low light. Then manually focus using live view at 10x zoom. That should be enough to make out bright stars enough to focus. Depending on your lens you might need to use either higher or lower fps. The higher the fps you use the quicker the screen responds so the easier it is to adjust, but you have to make it slow enough to pick up enough light to focus.
Lens sharpness is not really very important for astro, noise hinders your sharpness much more than the lens does. Focal length is the most important factor to consider when buying an astro lens, and it all depends on what you want to do, there are applications for just about any length lens from 8mm to 8000mm. Wide field timelapses: 8mm fisheye, nebula/galaxys: 1000mm telescope, planetary: 2500mm+ telescope.
I don't really care for all the night exposure time calculators. IMO just use trial and error and push the exposure time until the star trails are unacceptable to you. The amount of star trail you get also depends on which direction your pointing, which these calculations don't take into effect anyway.
For timelapse I usually shoot a little bit longer shutter speed than I would for non-tracked still photos, because when reduced to video resolutions, the star trails are less noticable, and also because the scene is moving anyway (kind of like desirable motion blur in normal video).
Sometimes it's cool to shoot timelapses when the moon is full or almost full. It looks like a daytime scene but with stars. You also don't have to worry about light pollution. So start there if you can't get somewhere dark (or it's the wrong time of the month, like right now).
