Q: If I delete all info on my old Mac so I can donate it, will it effect my new Mac?

Follow the instructions at > What to do before selling or giving away your Mac - Apple Support

Assuming you are migrating all your stuff to the new one first, then deleting all your stuff on the old one won't affect the new one.

As long as you moved (not synced) your data from the old computer to the new one, you're fine.

Which brings up a point: you do have a backup of everything on your computer, don't you? If not, get an external hard drive and make a backup - you never know when it suddenly becomes very important that you have one.

Agreed, and the backup is excellent advice