Tough decisions all rv owners had to make at some point. My wife and I shopped, saved and debated for three years before making our purchase. Definitely a wise idea to select the rv first, then the tow vehicle to meet the needs. As others suggested, you can never have too much truck. In fact, I will never own less than a 1-ton, even if we were ever to transition into a towable.
In terms of truck campers - the larger truck campers can work for four people, but tolerance levels (and the size of the passengers) have to be considered. Our short bed camper works great for our family of four, but when the kids are full-grown, it may be a different story.
I've never used a pop-up camper, so I'm not sure how they perform in the cold weather. However, our hard-sided has been used in all conditons and has kept us quite comfortable.
Good Luck with your decision. Note: Judging by the start date of this thread, you may have already wrapped up a purchase.