Looking to replace all the old and dry vacuum lines such as the ones coming out air filter box, map sensor, brake booster, etc. Anyone know what size and best place to get quality ones? Should I see an improvement in overall performance?
Your best bet is to take some of your old hoses to an auto parts store and try to match them up; remember, your hoses are metric, so SAE hoses will be either too tight or too loose. Some stores carry both metric and SAE hoses. The larger hoses may be form fitted for which you might have to go to a Nissan dealer to get them.
If any of your cracked hoses are vacuum hoses, then replacing them should improve performance by virtue of eliminating a vacuum leak in the intake system.
The vacuum hose size is 5mm (3/16-inch). I got silicone vacuum hose for my Frontier off of Ebay. Besides being more durable, you can get them in different colors besides, but still including, black. I found blue hoses that matched my NGK ignition wires. It's also not expensive for a decent size roll of it.
For the booster hoses, unless there is a problem with them, I would leave them be or replace them with genuine Nissan parts. They almost never go bad and they are molded hoses.