Ep1 Session 1 Rules Notes

Can characters utilize deceptive attack while using a missile weapon?

No

Can characters cast an another spell or attack while concentrating on another spell?

Yes, here is the text from the concentrate maneuver:
Focus on a primarily mental task – spellcasting, activating an ability that calls for this maneuver by name, or using a noncombat skill (like First Aid or Intimidation) in combat – even if this has a minor physical component.
If your activity requires multiple, successive Concentrate maneuvers (e.g., a spell that takes more
than a second to cast), you must make a Will roll at -3 whenever a distraction occurs. This includes anything involving an active defense or resistance roll, or injury, restraint, or being knocked down. Failure
means losing your concentration – start over! Movement: Step.
Active Defense: Any – but it interferes with concentration as noted above.

In the case of Shape fire, it also only takes a Concentrate to move, not to maintain.

Should the spiders have been a bit more dynamic and harder to kill?

Yes.  The spiders technically had a range C (close combat) bite, which means that the spiders should have been virtually on top of the characters, forcing the use of movement or range C weapons only (knives, fists, etc...).  They also perhaps should have hung back and used their stealth / climbing to attack the more lightly armored characters in the back rank.  The use and effectiveness of the webs should also have been more apparent.

Can I craft items picked up from fallen foes, in particular weaving spider silk garments from spider webs?

In particular no, but in general maybe.  more to follow