Yes! The ceremony is outside but dinner will be inside with optional outdoor activities such as lawn games and campfires happening during the evening. Check the weather and bring layers! October in the mountains can be chilly!
The last bit of the drive to the venue is unpaved. Allyson's Honda civic handled it just fine but if you've got options, you'll probably won't to drive your more "robust" car :) Venue parking is on a grass lawn and there is amble space plus handicapped parking if needed!
It's really whatever you want it to be! Dress code language can feel confusing but from what I've seen online dressy casual/casual is probably what most folks will go with. Ultimately, we'd just recommend you wear something you are comfortable in and remember to bring an extra layer if you decide to be outside in the evening.