You don't even have to move them all. You could literally send a tiny amount of dust from an address with a large amount of btc and that address would no longer be considered "abandoned".
If you spend from any address any amount of coin, even if not the whole amount, then the public key of that address becomes known, and could be an issue (small, maybe negligible). The reason you want to use a new address every time you move coins (and the change address is new also), is so that the new address does not have the public key known yet until you spend from it.
Since you are signing with your private key anyway, why not just move the whole amount? Discard and do not reuse the old address anymore.