welcome to the great wide world of hilarity and misery that is DF.
I can't believe I was able to drain a lake and make a big mud room to grow mushrooms. AWESOME!!
try this with a brook/river someday and watch the fun unfold!
every DF player should have had this experience.
It was even better in 40d. Not only was there water running around your corridors, it was laced with vicious fish.
The carp were really well known for pulling dwarves in and generally slaughtering dwarves.
Also, be careful of the caverns, but don't be too afraid of them. If you have to, remember that constructed floors and walls are completely indestructible.
Indeed, I believe the wiki used to say on the 40d construction page (it might still) that it is completely normal to have a magma cistern made out of wood. In fact coke/coal walls and floors didn't ignite either via magma, though I do remember from experience that, if done right, you could get burning coke floors. I think it involved melting an ambush and trade caravan under a magma waterfall to get that.
Anyways, Sober, I take it you're playing DF 31.xx (also known as DF2010)? I look forward to hearing about you exploring the caverns.
Edit: Also, there's no shame in using a tileset, I use a rather simple one myself because I couldn't stand not having square tiles, and I liked the shape of the smoothed walls. You need to find one that you like, for example, some of the simpler ones with thin lines give me a headache.