There are a number of good options against 1. e4. The most popular is the Sicilian 1.c5. I personally play the French defense against e4. There is a opening explorer here, but free accounts only get to see up to move 5. 365chess has a good opening explorer that you only have to create a free account to see passed move 5. You can explore different opening systems, and see what you like or don't like there. Here is the link: https://www.365chess.com/ . Also word of caution with the Blackmar-Diemer Gambit it is not a sound gambit, and is not played at upper levels of chess. I have a friend who played it for many years, and he got up to 1900 USCF, but could not get much higher until he changed his opening system away from the Blackmar-Diemer Gambit. If you like playing it then go for it, but you may have to change up your opening system eventually if you plan and get up to the class A or expert rating to range to go higher.
Openings for black other than e5
Chess Openings Tier Lists by GM Hikaru Nakumura and IM Levy Rozman
Chess openings are rated in terms of their appropriateness vis-a-vis player skill level - i.e., beginner vs intermediate vs GM’s, etc. For each of the openings discussed be sure to pay attention to whether the evaluation is from White’s or Black’s perspective. They also frequently refer to some openings as "garbage" or "bad"; these qualifiers are used in the context of, for example, how much so-called "theory" (i.e., documented variations) the opening encompasses, or how much emphasis the opening places on positional versus tactical skills in order to play it well. For example, an opening they refer to as "garbage" (an unfortunate choice of terms) for a beginner may in fact be appropriate for higher rated players who typically know more theory for the openings they play and have a more highly developed understanding of positional concepts.
The Chess Openings Tier List for Beginners…
https://www.youtube.com/watch?v=M9CwH47r6og
https://www.youtube.com/watch?v=fHsb7-LbC34
https://www.youtube.com/watch?v=z3FBRlzSMHc
The Chess GAMBITS Tier List for Beginners…
https://www.youtube.com/watch?v=S9N6Bo7BBPg
The Chess Openings Tier List for Intermediate players...
https://www.youtube.com/watch?v=Qq_rEYTiLy4
https://www.youtube.com/watch?v=mCVdrmKHdiI
https://www.youtube.com/watch?v=Pblb8ZQ3OJ4
The Chess Openings Tier List for GM's...
https://www.youtube.com/watch?v=glMp0dNGPN4
https://www.youtube.com/watch?v=3vzDjlu-96s
https://www.youtube.com/watch?v=HShiBcGbfeA
Chess Openings Resources for Beginners and Beyond...
https://www.chess.com/blog/RussBell/openings-resources-for-beginners-and-beyond
https://www.chess.com/blog/RussBell
I think I have a good opening repertoire when I'm playing with the white pieces, after e5 I've been playing the Vienna Game, if the opponent plays the Scandinavian I transpose it into a Blackmar-Diemer Gambit with d4, if they play the sicilian, the french or the caro-kann I just follow the main line. But I don't really know good openings for black after my opponent starts with e4, I usually answer with e5 and keep developing my pieces naturally. But I wonder what opening you guys who are reading this like to play with black, there are just so many openings that I don't know what to play and feel overwhelmed sometimes. Which opening should I learn for black after e4?