If Arsenal host PSG humbly, they will be able to get good result but Arsenal must know that even a draw in a first leg won't be too bad result. Having an acceptable result from a first leg will give Arsenal multiple tactical choices in a second leg in Paris. Arteta seems to be a careful and well-minded coach but it will be up to his players too.
Arsenal will not be rash when hosting PSG tonight they will be quite careful in this first leg match because they are important to win especially in a large number of goals.
I think in the first leg if the result is a draw then the possibility of Arsenal will be difficult in the second leg at home to PSG, so as much as possible Arsenal must win tonight at least it would be better.
Doing with BTTS I think it is quite more convincing for the semi-finals this time although it cannot be denied that for these 2 matches it will be very difficult to determine but overall I am also doing the same thing as what you are doing right now.
Hoping that with a bet BTTS can win, then the next day Barcelona win... then we're happy. Lol
But many people say BTTS is better than 1X2 betting.