I want to change my baseboard and window color can I paint over a cran

you will have to use a primer

You should spend most of your time preparing a surface before painting, much more time than applying the paint. If you don't make it clean and remove the gloss from the old finish there is a very good chance that the paint will start coming off.

You may have to paint with Kilz first to cover the dark color.

You will have to prime first - I would recommend 2 coats of Kilz and then 2 coats of your topcoat color.

Absolutely--one of the many wonders of chalk paint! Probably will need two coats to get a clean white. If leaving it with just chalk paint-don't forget to seal it with a wax-but since it is a window and prone to temperature changes possibly, I would seal with a urethane-semi gloss

I would not use chalk paint - I would use oil based primer and paint instead.