Reddit mentions of Book of Challenges: Dungeon Rooms, Puzzles, and Traps (Dungeons & Dragons d20 3.0 Fantasy Roleplaying)

There's a similar thread here. If you've got the cash, you could try Grimtooth's Traps or The Book of Challenges.

http://www.amazon.com/gp/aw/d/0786926570?pc_redir=1410497506&robot_redir=1

> Goblins

Actually, I think they'd be more likely to strike as soon as the party makes themselves comfortable - as in, they settle down for the night - after clearing a large infestation.

> Recruiting soldiers at different cities

1. Don't forget to implement Charisma checks (Diplomacy) for recruiting soldiers. A well-spoken, seemingly good leader will be more efficient at recruiting than a completely uncharismatic Wizard.
   
   
2. Keep in mind you can hire a dozen spearmen at any village for a barrel of mead and a gold coin, but given enough time you'll train them up to elite levels. Provided they don't skip fortress (which seems realistic). Recruiting experienced soldiers at cities will save time, but not gold in that case.
   
   And, IIRC, pay for a trained soldier is between 1 silver and 1 gold coin (1 gp = 10 sp)... at least in 3.5.
   
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   No idea what edition are you playing, but Stronghold Builder's Guide has plenty of material not restricted by editions. Book of Challenges also has a pile on info for making in-built castle and dungeon protection mechanisms (read: traps).
   
   Finally, take a look at Stirling Castle, Scotland. I came across it fairly recently, been drooling ever since. It looks amazing. Only needs some adjustments for a fantasy setting - for example, protection against flying enemies.
   
   Happy DMing! :)