at the 1500 - 1600 level is it necessary to have multiple responses to say e4?
No.
I'm worried this approach may not work, as well because people will learn I play the Alekhine and prepare super well for it
First of all, you're not playing for the world championshp 
not many will prepare for you, and those who do won't prepare a lot, so don't worry. It's more likely they will think, oh, I forgot the alekhine opening exists, I'll be sure I know a few moves before I go to my next tournament.
But also... this is how tournament chess works. You can't expect to surprise your opponents every game. You will inevitably face opponents who are not surprised by your openings. The better you get, the stronger your peers will be, so more and more they will be competent well rounded players. The goal of the opening is to get a middlegame position you enjoy. An opening isn't supposed to win the game for you.
Is there a way online to scout my openents who are USCF members to see their games
You can type their first and last name plus the word chess into google and sometimes that will give you games.
You can also buy databases like chessbase, although preparing for your opponent that way isn't very common U2200.
... and the effectiveness is questionable. In fact I knew one master who purposefully played his 2nd rate stuff when playing in certain tournaments where he knew his games would be published in these databases.
(we all do)
If you are playing long time controls it would be crazy to not know which lines you prefer at the very least... I would suggest alekhine is a great choice as it is forcing, sound and rarely encountered. You will know it much better than your opponent and only in a small minority of your games will they play critical lines to move 10.
Study the lines a little bit... Play it in blitz... Check where you went wrong... You will get E4 nf6 on the board in 30% of your games and learn very fast!
10 moves deep isn't very deep in the Alekhine. Remember, that knight gets moved two or three times before either side even start to move pieces off their back rank. By the time the position just looks 10 moves deep, in comparison to another opening, it's more like 20.
I learned the exchange variation fairly well before I started playing the Alekhine with black. You will run into players that know the line they are playing much better than you do. The thing is, you're having to learn every line and white is only having to learn one. Of course white is having to learn a line against every possible black defense, but that is idealistically. In reality, people neglect one area of study and over do it in another. So some people you will run into, and they know nothing about the Alekhine Defense, and then there is that one guy that knows nothing about the French but everything about the four pawns variation against the Alekhine Defense.
A lot of chess players choose a defense based on the false premise that their opponents won't know it as deep. The more and more you improve, and the better and better competition you play, the better and better they are with the white pieces.
I can remember playing a guy and he was beating me so badly in the Nimzo-Indian, I asked him if he was cheating. Of course he was angry, but the next game I switched to the Grunfeld and obliterated him … well, that answered that. He definitely wasn't cheating. I suspected that maybe he also plays the Nimzo and maybe that's how he knows so much. No … after checking his games in opening explorer. That was not the case. He must have just specialized in stomping the Nimzo-Indian Defense. Maybe his/her abusive step father played the Nimzo and he/she was on a life mission to trounce everybody that played it against him/her. Who knows? But the person was lower rated than me, didn't play the Nimzo with black, but knew the opening much better than me.
Some people just have an expert or chess master friend and playing against this friend will cause them to have to know specific lines very deep.
I don't play the Alekhine as Black, but as White, forget 2 or 3 times, most my games, the Knight moves the first 5 times or 5 of the first 6:
1.e4 Nf6 2.e5 Nd5 3.c4 Nb6 4.c5 Nd5 5.Nc3 Nxc3 OR
1.e4 Nf6 2.e5 Nd5 3.c4 Nb6 4.c5 Nd5 5.Bc4 e6 6.Nc3 Nxc3
Occasionally I get someone that doesn't take on c3.