By the way - Krabi Immigration is not in downtown Krabi Town - nor near the airport. It is actually near a big river pier along a long and large avenue of Government buildings. The Government building avenue is newly renovated with street lights powered by little windmills and small solar panels. So you will know if you are near it. You can find it using Google Maps or if you have problems just flag down a motorcycle taxi and have him take you there or lead you there. It won't cost to much.
Your Krabi Address is likely to be enough. Just have it written out. Krabi / Ao Nang is a very active tourist area. Krabi Immigration sees a zillion tourists a year and are fairly leinient unless you have a passport full of Exempt Entries and Tourist Visas. The Immigration office will not likely have an excessive queue. But Monday - Tuesday - Wednesday are the only days open next week - so crowds could be up.
You can't really drive into Laos without a lot of documentation, insurance and hassle, so I recommend the Kiengpiman hotel in Mukdahan, Thailand - drive in the evening before - leave the car - get a tuk tuk next morning to get to the bridge to Savannakhet.
For those under age 50 to get close to a year (up to 9 months) ... You can get a METV - Multi-Entry Tourist at a Thai Embassy/Consulate in your home country. Qualifying requirements are on the website for the Thai Embassy / Consulate in your home country.