if you use adv world gen you can set minerals a bit better. Chalk is actually pretty nice: it has bauxite, which I think is magma safe and has deposits of hematite. In short, it's an iron ore and magma safe stone containing layer of flux stone.
iron and flux is most common in sedimentary layers. Sedimentary layers are most common in areas with low volcanism. Fiddling with the volcanism settings (weight) so they're a bit lower will greatly increase the number of flux and iron embarks. I've had no flux occasionally, but Iron every time now. Going for areas with deep or very deep soil will increase chances, but also increases chances of finding aquifers.
I'm agreeing with nenjin on not being patient enough. I usually have so much going on still, preparing for the first siege, while I have a quarter of my fort at non stop training.... Well, I know I'll win, but it's definately not the cakewalk it is by year 8. I usually lose a dwarf or three due to ambushes anyway, but when the sieges start picking up pace, it can get messy. All the cages sprung, all the traps jammed and a rutherer standing on the bridge so I can't clean up.
And this is also one of the things you have to decide. How dificult will you make it for yourself? I can make as many as 4 pathways into the fort. One allows wagons but kills ambushes, one allows elf caravans but kills everything not trapavoid, one that kills everything that can't fly, one that kills everything that isn't magma safe. Though add some water and it kills everything. Setting it up is fun, no doubt about that, and it usually takes a very long time to make, but after that? So I limit my options myself. I have the caravan road always. The question is a dodge trap with spikes or weapon traps. One is a hassle to set up and has to manually operated, the other doesn't work against trapavoid creatures, neither works that well against flyers. I'm still almost guaranteed to win, but it might cost me a few dwarves when someone does break through.
You can do more, sure, that's why it's called a "challenge". There are dozens of challenges that ask you to limit yourself in one way or another. No danger room or other exploit, no building underground except dungeons, storage amd mining and make the living quarters and such above ground. Make an actual usefull siege battery. You name it, you find it.