Any good oral rinse will do not too much coloring or flavouring as they can cause issues. You won't be rinsing for too long just a few seconds, it's just to keep the bacterial levels in check nothing more.
You can rinse your mouth with warm salt water if you have a lump appear after you take your tongue ring out. If the lump continues to get bigger and bigger, you should seek medical attention.
The answer is No.
it doesnt matter
You will have good breath and a healthy tongue. You're supposed to brush your tongue and rinse your mouth with mouthwash when you brush your teeth.
Generally the tongue will prevent that from happening however it's still wise to rinse with a good mouth wash after you have removed the barbell and consumed anything, just to be on the safe side.
I don't have a white ring under my tongue.
There is no "lock on a tongue ring" and it's not a ring it's a barbell.
If you have a tongue ring, it makes it hard to make out. the ring always gets in the way.
Google search for "18 gauge tongue ring"!
The same way you did before, except now you have a tongue ring.
It can only make you sick if the ring is not thorougly hypoallergenic.