Donnie, big is always better

More stable and you don't run out of room. The mandarin would require a good sized tank plus a refugium as they tend to starve without live pods. And you'd need to run the tank for a few months to get enough pods for it to do well.
Not sure about the lobster 'cause I don't know what kind you mean, but I've always thought they were pretty good predators, your fish could be in trouble.
If you buy a reef-ready tank, the overflow is already built in to supply a refugium or sump below. If not, you'll need an overflow box to do the same thing.
Oh yeah, your lights are adequate for many easy to keep soft corals but the bulbs would need replacing - most bulbs only last 6-9 months before the spectrum changes and they become less usefull.
Good luck