To OP:
1. It's only really harder on hills. Flat surfaces, I hardly notice my trailer.
2. This mostly depends on whether or not you have space to keep the trailer fully assembled. If it's fully assembled and sitting in your garage, it'd take 10 seconds to attach it to your bike. For me, I have to keep the trailer in my basement (townhouse without a garage) so it takes me a couple minutes to set the thing up, then attach it.
3. My trailer has a mesh screen for general debris, and an optional plastic cover to cover from rain.
4. Conservatively, going super slow, possible traffic stops, I'd say you'd be to work in 10 minutes tops.
Instead of starting a new thread... I'll ask a few here too.
I have an older heavy GT mountain bike. Is it worth spending the money for new street tires on it? I only paid $115 for it. I'd really like something lighter for my commute..is it worth selling to look for something that is lighter and more road friendly?
A lot of variables to answer that question. Are you pretty much 100% riding on the road (and not doing dirt trails)? Slimmer road tires would be a huge boost. Is it worth selling? Totally depends on your financial situation, and how many miles you're putting on the bike. If you have a shorter commute via bike, I'd say get new tires and see how it goes. If you're riding 15 miles each way, and long rides on the weekend, I'd say consider a new(or used) hybrid.