The fish is a Bicolor Blenny (Ecsenius bicolor). It is the type of fish that is suitable for nearly any tank, and gets along with pretty much any type of fish. Not aggressive at all and perfect for a 55g community tank. Huge personality fish.
Getting juveniles is a nice idea but it doesn't work. Fish can grow fairly quickly (a matter of months), sometimes juveniles can be more delicate, you get attached to them and re-catching them can be stressful for the fish and often results in you having to remove all the the live rock to re-catch them. My advice is only get a fish that could live in your tank at adult size.
There are usually alternatives to certain fish. For example instead of a Yellow Tang (if you want a bright yellow fish) you could get a Yellow Angelfish, or maybe a Yellow Wrasse. There is nearly always a fish that suits what you want, and that will fit in your tank.
Anemones are difficult to keep, they need a lot of light and good water quality. You should only really look at getting one once your tank has been up and running for 6 months. Anemones are bought, like a coral or fish, and they have a muscular foot that attaches to the live rock wherever they are happy.