Maze is pretty much a gold sink : you can't expect it to refund your investment over time, since it it will reset granite and all your rooms every major patch or so. All gold invested will be lost every 4month (rough estimate). But you keep the defenders/traps/auras over each reset (at least i hope it works like this).
As a new player, set it up so it can defeat parties of reincs or lower level players. Just use the rooms you're allowed to, then it can be done with a couple of well thought rooms and auras and traps. There is no magic rule since the spots you get in your maze (blue, epic, leggy) are random. Investing in a bossy seems overkill though, unless you have a leggy spot in your maze ofc.
If you want your maze to defeat top groups, it will cost you much much more time/money because you'lll need best defenders (from astral or raid or cash shop), best traps, and up your rooms with a lot of gold as well as your defenders rank with your gearscore. Remember that any gold spent to upgrade a room will be lost when it resets.
Basically, unless you run for the maze title and reward, you don't wanna do that because it will cost you much more money than it willl ever bring back.
If some party tries to rob your maze, you will lose supplies needed to activate auras/traps in each room, and if they succeed to clear all maze your horns will be stalled for 3 days. You don't actually lose anything (they won't steal the gold in your bag), except days of production on your horns.
Hope it helps
Cheers,
Poch