Can I do a border bounce to renew my visa exemption in Thailand, and how long should I stay in Laos?

As the team have explained. Only need to do a border bounce in Laos if you want to visit Laos or you have already done two 30 day extensions. So a local 30 day extension easy peasy for you

Go to the local immigration office and do a 30 day extension for ฿1900.

Make sure you've had a tm30 filed for that province.

The immigration personnel at Nakhon Phanom are very helpful and easy to deal with.For 1900 ฿and 1 hour a lot easier than taking the bus to Laos.

You can do the 1st 30 day extension at any immigration office.

You are going to do border-bounce, there is no "visa-exempt renewal".

Q1. The visa exemption renewal is it still of 30 days when you are entering in Thailand by road ?

-> Visa-exempt entry for French passport holders (and other 54 countries currently) is always 30 days regardless of entering by air or land.

Q2. How long time i've got to stay in Laos before re-entering in Thailand ?

There is no minimum stay out of Thailand to re-enter. Technically, you can do border-bounce in one day.

Just be aware, you only have 2 visa-exempt entries by land per calendar year.

If you haven't applied for 30 days tourism extension on your current entry stamp yet, you can apply for it at the local immigration office where you are staying for a 1900 baht fee.

1... The Visa Exempt Entry into Thailand is 30 days.

2...You can do a BORDER BOUNCE and reenter Thailand SAME DAY.

As you plan on doing the border bounce to Laos...no problems.

AND...For those who are thinking about doing One at Poipet Border Cambodia. DON'T... AVOID POIPET BORDER CROSSING.