How many minutes will the train be late?
would be ok. From is incorrect in this question.
From how many kilos does she slim
I'm not sure slim can be measured like this. Your best bet will be How slim is she?
Generally, you'll be just putting how in front of the question and changing word order accordingly to make your sentence a question.
She has many friends.
How many friends does she have?
If there's a preposition somewhere in the statement and it is connected with many or the noun, you'll want to move it toward the end.
I've heard this rumor from many people
How many people have you heard this rumor from?
Notice how from is separated from many people and put in the end of question. Strictly speaking, From how many people have you heard this rumor? is also ok grammatically, but in my opinion it is a little more awkward.