To put down planets, you first have to place stars and then place the planet/s near them. To set the planets as homeworlds, you right click on them and set it up on the screen that appears.

As to your second question, that isn't possible, savegames and maps are completely different formats.

AFAIC, this is Stardock duty to take.

Text based, in the usual "Help" menu option. Not some bink videos about gameplay "suggestions" or demonstration.

Simple snaphots of UI along with descriptive tags for each elements can go a loooooonnnnng way into explaining what sort of features these editors offer to the casual gamer.

They'd have to pay me to do that much work.