Eazeh's page

So, I've been running a few games for some friends, and decided to write up a homebrewed campaign. Problem is, I've never done this before, and I'm not sure how to get started.
It's not a sandbox or anything, so it's going to be fairly straight-forward, but other than a few set-pieces, the BBEG, and a general plot-idea, I've got no clue how to start writing this.

Two ways I can see it working would be to write the set pieces, the main encounters, etc, and then link them together with logical connections, and add in a few random encounters or something.
The other way would be do it step by step, writing each part as it would be played through.
Any opinions, help, advice etc?

So, I have three questions, and hopefully I'm posting in the right place.
First up, I've never had to deal with prestige classes in games I've run before (not like I've run many games though).

The druid in my group wants to become a mammoth rider, he's got a wolf companion, 9 ranks of handle animal, 9 ranks of ride, 5 ranks of survival, and believes he'll have a BAB of +6 by 8th as a druid. I can't see anything that says he's wrong, per se, but I'm pretty uncertain, since like I said, I've never dealt with prestige classes before.

The fighter in my group has a similar problem. He's LG, wants to beome a Hellknight, has 5 ranks in intimidate and 2 in Knowledge (planes). Since a bearded devil has 6d10+24 for hp, he thinks he can kill one at level 6 (provided he can find a Hellknight to watch), and thereby qualify for the class. Again, I'm not entirely sure, since it's got HD equal to his own, and a flat amount extra, but not definitively greater. Would killing that on his own count?

Other than that, my players would greatly enjoy a campaign with demons, devils, planar entities or similar, but I'm having trouble finding free ones suited to the levels they are/will be soon (5-12ish?). Other than making one up myself (which I'm nearly resigned to doing by now, having scoured paizo.com's free pdfs and such), could anyone recommend something? I don't have terribly high hopes for this one, lol.
Oh, and just in case it's important, I'm using d20pfsrd.com for most of this info... the bits I can't find in the books, at least.