For a trap, simply choose an appropriate mechanism from the lists on p. 339 (not sure if you have a horror or mechanical taste) choose a level of difficulty (Threat Level 2 yields 11/16/17/22 DC's), a level of concealment, (you roll this against their Notice/Search) and an effect. For first-timers, you might want to softball them with some light damage, but I found that the sickened
quality is easy to track (-2 to every d20) for first timers as well. Don't forget to add the XP column values and multiply by TL (2) at the end for every character.
You want more than one fight, eh? A Standard group (or two, or three) is an easy way to try out combat mechanics for you and your players. I'd suggest monstrous insects(p. 275) since your characters are likely not to want to reason with them, and they're likely to not want to reason right back.
The Skeletal Men-at-Arms(p. 294) are probably fine as they are in the book, but you can give them any equipment you want up to Complexity 15, and alter their ability blocks using the NPC creator
For the Zombie Knight, start with the Risen Template,(p. 293) and add it to the Man-at-Arms or Knight "Rogue" NPC's. Give him any special abilities you want to really see in combat. If the tomb is large enough to accommodate a horse, add he Skeletal or Zombie Template to that, too, if you choose knight. If the tomb is small, use the Warlord "Rogue" instead, though they are worth decent XP.
Statblocks: If you don't have a lot of time, use the NPC Converter
to make transform their blocks into usable numbers, instead of Roman numerals, but don't forget all qualities need to be added manually, and damage save penalties for size aren't included.