All good questions.
1) Existing Defenses and Housing
- Very little at the moment. You are located in a large underground cavern very deep below the surface. This cavern once held a small First Dwarf outpost, but it's limited mainly to the central stockpile as far as buildings are concerned. And that was erected by the Griswine Dwarves. The wood which composed most of the buildings here has rotted away centuries ago, leaving only dust behind. The main dwarven settlement was located in a distant cavern, and was lost to the horrors of the deep before this outpost was abandoned and the dwarves fled these lands. There is more than enough space here to build a small metropolis. There are four tunnels, one in each cardinal direction, leading out of this cavern. A small waterfall and pool can be seen in the northwest corner of the cavern and serves as a clean water source.
2) Protected Farmland or Minerals
- Kind of. Each of the farmer and miner units can be turned into a Farm or Mine building. They aren't normally available units, you would just build the respective building, but it didn't make sense for you all to carry buildings with you. When you activate one of them, you gain a farm or mine of a local crop or material. For crops if there's something specific you want that doesn't have unusual properties, feel free to ask me for that crop. Most likely it will be cool by me and your farmers could have been carrying their seeds. As for them being protected, the cavern here is flat and smooth. There are currently no unique features except the waterfall and the tunnel. So, while they don't currently exist, using a miner unit procs an event like "Your miners have spotted copper ore in the walls of the cavern, and have set up a mine to extract the ore!".
3) Instant Food
Farms built this turn will produce food this turn. There's not a good IC reason for it really, just a balance thing. One farm produces 1000 food.
4) Hunters
Under optimal conditions hunters can provide 2000 food. Their haul is determined by a d20x100. Then any special random or ongoing events may add or subtract from that number.
5) Armies
Armies are composed of 50 soldiers. They and other units are included in your citizen count.
6) Making new units
Yes, but also no. It takes 100 food plus any required materials or tools to make a new army. So theoretically you could set up additional farms or train additional hunters, but it would cut into your food and they wouldn't be able to take action until next turn (because it takes a turn to train units/construct buildings). I'll add a list of available units and costs to the OP.