Alright I play SSBM quite frequently for quite a while and have some good knowledge over the game and the way of smash and mabey a intermedimate myself with Marth and progressing with Fox so mabey my opinion will matter some. lol
With your mipkahu comes a arsenal of good aeriel attacks that can be combine with a short hop and not necessary a L-cancell is needed. You are letting the computer walk into your Fsmash which can be good but won't happen with a human so go to training mode with 1/4 speed and practicing some grab to tilt to smash combos. Wavedash doesn't work so weel with pika so dont' wrry too much about it but learn to know how to use it if you dont' already.
On the good side of life: You are fast and can preform the moves as the enemy is entering the hitbox of pika which can help because pikachu is a very short range character. And you also knwo to switch your moves up every now and then.
Some very important tips to learn are shield grabbing which is shielding and thne pressing " A ". The most important tatic probably to chain grabbing or just grabbing in general. I hope I helped and please make more because I love to rate fellow smashers.
I would make a video of myself but I don't have a camera. :(
keep smashing man! You have some potential :P