A mandarin won't live long term, nor will any other dragonette in that size system unfortunately. There just isn't enough live rock to support the pods the mandarin needs. If you were to purchase an ORA Mandarin that has been trained to eat frozen, you'd have better odds, but I still don't necessarily think it's the best idea.
Flame angel is also too big for a 29G. An African Flameback or a Pygmy (Centropyge argi) would be better, as they stay a little smaller.
Do you want a sand sifting fish or anything that will keep the sand "clean". The best option would be some Nassarius snails. A small goby such as a Yellow Watchmen will sift a little, but not too much. Some gobies, such as a Sleeper Banded Bullet and the Diamond Goby will sift too much and deplete your sand bed of beneficial fauna that helps break down unwanted debris.
Some other fish to consider are some of the smaller flasher and/or fairy wrasses, blennies (they really have a lot of character to them, even the small ones), firefish, Dottybacks, Basslets, etc.
