Several months? The new (save breaking) version is expected to come in a few weeks, so you might want to consider waiting for it before beginning.
... why?
This is a project that can be done now, with this version. The future version, Toady himself says will probably be fairly buggy, and he expects to have to patch up in the following months. Plus we don't even know when this new version is going to come out - it's roughly whenever Toady feels the most egregious crashes to desktops have been quashed. And that could be a month or two in the future.
Inspiration doesn't linger forever. Strike while the iron's hot.
I probably won't go for magma falls outside as I am not good at such things and I think it is an invitation for disaster-ordinarily, that would be fine, losing being fun and all, but I think in this case it would be an annoyance as I will probably be devoting several months of time to this project. I was thinking the main structure would be made of bauxite, while the entrance to the temple will be encased in obsidian.
Well, if you're too nervous, do it in limited amounts, and make it a learning project. Keep seasonal backup saves, just in case you need a rollback.
Still, it shouldn't be TOO hard, so long as you keep a nice resevoir. Magma isn't pressurized, and if the resevoir you pump from has no extra magma feeding it, and you don't put any floors near the waterfall, there is little direct danger. You basically just need a basic pump stack (
see diagram here), which then pours magma out a chute out the side of the spike/spire.
Also, to make the spikes appear "angled", make "circles" of stone, which will get narrower every 3 to 7 floors, depending on how fat or thin you want the spike, but make the center of the spike shift in a given direction every handful of floors up, as well. Put ramps on everything you can, so that it looks cool in Visual Fortress.
If you make a spike angled at a convenient angle, you can make that magma pump stack take place inside a spike that is actually vertical along one side.