1 d4 d5 2 e3 Nf6 3 f4 Bf5. Black has developed 2 pieces, white none. White has a hole at e4 and 2 black pieces Nf6, Bf5 as well as pawn d5 look at it.
prep against d4 d5 e3

Actually for those of you saying an early Bf5 is ok, the best stonewall move order is 3.Bd3. So if black wants to stop this, he has to play 2…Bf5, when white has the option to transpose into the modern quiet line of the Slav with c4 and Nf3.
If black plays 2…Nf6, white will play Bd3 and follows up with Nd2, c3, and only then will he play f4.

The position is still playable for black and yes there can be many variation i just gave him a sample line
And yes lot of time black is better lot of time white crushes with a kingside attack at stone wall is a good opening and i can't give a clear cut solution to that
It just depends on move
You can only prep for slight advantage and what are your key plans as black against a particular opening

But if bishop trades it gives a God clamp for our knight but the pawn structure is compromised
Anyway both the lines are good with some slight advantage for black and thats what you can hope for and now you have to play a game of chess and not to blunder

He could, but you can always play h5 and utilize the e4 hole. In any case, if white had to move his bishop twice it's probably a concession of sorts
Here are some Chess openings you might like : https://bit.ly/3JPGykn
why is that a bitly link can't you just post the normal link
https://rumble.com/vyue2q-agressive-chess-openings.html here you have
hey guys ! do you have any prep against ( d4 d5 e3 and whatever black does after e3 white plays f4 ) ?