oh its not hard to CG Ike, its only nerve wracking due to input lag that gives you a leeway to jab before we can grab you.
dthrow is not a CG on Ike (Only 4 characters get CG by it), just jump before landing. But dthrow to utilt works at low percents.
Pikachu wouldn't really QAC to you, if he loves to (and is predictable about it), do Usmash to hit him.
Pikachu is a lightweight sooo, utilt kills early, fair wrecks Pikachu.
Be careful though, Pikachu can do some nasty edgeguards like QA edge hog, QA through you when you try to Aether thus stunning you and screwing you up, and tjolting you. Thunder walls work well to. Tjolt can really prolong you while recovering if you keep hitting it during aether.
DO NOT PICK HALBERD!!!! The hazard part of the stage is impossible to come back to with aether against Pikachu. Tjolt will encircle the ledge and with multiple tjolts constantly circling it, you will never grab on it. Also low ceilings makes it easier on Pikachu for his thunder.
Corneria is a good stage for Pikachus well. Tjolt/thunder heaven.
Luigi's mansion seriously hingers Pikachu.
Spiking pikachu in the water won't always work since Pikachu can QA DEEPER into the water to avoid spikes.
BF is a great stage to CP against Pikachu, but smart Pikachus can utilize platforms to hit you from the other side with tjolt and to QAC onto, and thunder in between gaps to throw you off.
Yoshi's island does well as a neutral against Pikachu.
Lynat is great for Pikachu. Tilting helps tjolt, although it may screw around with CG, i never needed to CG an Ike with the combos i did anyways.
(utilt, utilt, utilt, uair, nair does like 40% anyways)
down smash provides a tech chase (For the smart people who SDI) otherwise try to shield half of dsmash than spot dodge the rest to punish effectively.