How to properly use the London?



Does being "closed" and being "sharp and tactical" go together well?

This is an opening with NUMEROUS books published on it. Given what you have said, I would suggest one that explains ideas rather than giving reams of lines.
You should invest in "The London System in 12 Practical Lessons" by Oscar De Prado.

Does being "closed" and being "sharp and tactical" go together well?
The London is not Closed, but yes, the two can co-exist. See the Classical Kings Indian!
Memorizing the first few moves of an opening sequence does not mean that you have “learned” the opening. The opening prepares for the middlegame. You need to look at a few books or courses on the London to see what the typical middlegame plans are. You could also search the database for games with the London. Playing through 15 or 20 games by Carlsen would give you a good feel for what can happen.
How you learn to play the London is how you learn to play all D-pawn variants!
You study the pawn structures and the themes! You study the how the minor pieces can move around the structure to launch attacks, you study typical themes that Black will play, study how Black's minor pieces will move to attack you, You look at the pawn formation as to where to open up files for your heavy pieces. You study attacks like the Pillsbury, the Greek Gift, the Stonewall attack and how it relates to the pawn structure and you study possible endgames what to move towards (like a 3-2 pawn majority on the queen side) and ones to stay away from.
If you do this you will discover a lot of ideas/plans ... when you get to a position where Black is equalized... then it comes down to WHO understands the position the best.
I'll ask... "Is the position really equal, if you know 3-5 ways to launch an attack from it, and your opponent only knows how to defend?