My "Sparta mode" rules are:
-At least 50% of the total population must be serving in the military past the first winter.
-4 of the initial dwarves must start with several levels of Speardwarf/Armor User/Shield User. Use your best judgment but err on the high side. The other 3 dwarves may be leveled however you choose. Initial equipment should be whatever you choose, but for best results only 1 axe and 1 pick are required. (This fulfills the 50% requirement when considering the metalsmith.)
-These 4 dwarves must be conscripted no later than the 1st day of spring following your first winter. Prior to that they may be used for whatever is necessary to get the fortress set up.
-All weapons and armor are to be made of bronze or brass. (Yes, the Spartans used brass spears as well.) Shields should be wooden on maps with trees, bronze or brass on maps without. I generally use plate mail for the armor. No, the Spartans did not make a habit of fighting battles bare-chested.
-No traps, no siege weaponry, no crossbows.
-Most importantly, all fighting must be done in the shade.
I'm not sure about the "build everything out of expensive stuff" rule - on the one hand I can see how it helps to attract more migrants and the like, but on the other hand, opulence is so very un-Spartan. Since this is a roleplay setup, I'd leave it out and get your fortress value from making masterwork bronze plate mail and the like.