1) For Nitrogen, you really need to get it to go through the beer. There needs to be a very small amount of CO2 in the beer to get any head. At room temperature (20c or below) ther eis about 0.75 to 1 volumes still in the beer and that's plenty. You're on the right track with 38psi of Nitro, but you'll want to rock the keg on its side for at least 20 minutes (maybe less time if it's below 10c).
To serve, make sure your line length offers you the correct resistance length for the serving pressure. Most kegerators have beer lines that are too short.
2) Acids can have different flavors. Homebrew supply shops carry Lactic, so it's an easy thing to order. Pretty cheap, too.
3) Can't help, but there is a lot of experienced advice available.