Hi Angelique,
I can give you some perspective based on the first few hikes I've completed and my planning for the next ones!
1) Most of the trailheads are accessible with any vehicle, but there are a few ways to confirm. I usually check other Social Hiker hike logs, as one of the questions everyone answers after a hike is “Road Conditions” – the responses will range from “Road suitable for all vehicles” to “Road rough but passable” or “Road recommended for high clearance only,” etc. To check the hike logs, go to “Activity” –> “All Hike Logs” –> then you can filter by challenge and mountain! I sometimes also check road conditions but looking at recent trail reviews on AllTrails.com
2) I intend to complete most of these hikes simply as day hikes, but some might turn into more!
3) I usually check the weather and adjust my layers accordingly, but I tend to bring more than I need and if I get to the trailhead and decide I'm carrying too much, I'll leave a layer in the car. In January, this means I'm usually wearing long sleeves under short sleeves under a sweatshirt and am carrying a down coat, but if the temperature won't go below 50F I tend to leave the down coat at home. If it's ~55 or below at any point, I'll usually wear leggings under another pair of pants too. Gloves and a hat are a good idea in chilly temperatures as well, though a sun hat when it's warm is also highly recommended. Bottom line: layer up, but it's up to you what makes you the most comfortable!
4) Some trailheads will have restrooms, some don't but might have a rest stop along the drive. I usually pee before I get in the car and before I get on the trail, but if you gotta go, ya gotta go!