Personal choice for that tank would be a Fisheri angel! Fisheri's tend to be a bit expensive, around $50-$65, because they typically are collected from Hawaii. As US citizens collecting these fish, their wages are typically more then their Indo-Pacific counterparts, who literally make a couple pennies per fish. Or if a Fisheri is a little pricey, a Rusty angel would be a cool slightly more oddball angel.
The Bicolor is a great angel. It is one of the largest 'dwarf' angels out there, and IMO, a little more related to it's large angel cousins. Look at the overall shape, its fins, etc. As to a pygmy, aka cherub angel, in my experience, they tend to aggressive. Sort of an ankle-bitter dog syndrome, small and feisty. Mine beat up a Half-Black angel that was close to 3 times as long, and many times his body size.
To the time it takes for a tank to mature "enough" for an angel, it really depends on what you started with. If you added a ton of super premium live rock with tons of stuff all over it, your mature time is going to be much less then if you added almost nothing but completely dried and barren macro rocks, and dried sand. 7 months is a pretty good time. If you add 5 months now, this may bring me to another point. While I quarantine every fish, angels, of any size, are on my "absolutely must QT" list. Angels tend to be much like tangs, and if any fish are diseased, it's them. Dwarf angels also benefit from QT, as they learn that you are the "food god" and learn to eat prepared foods. After you setup and QT and put the angel thru the usually QT routine, you should be at about 7 months anyways!
