Thank you all for these responses.
1. I'm guessing that you could probably see those cities with telescopes and stuff.
1 and 2. I was planning on making the two planets pretty close to each other, closer than the Earth and Moon are to each other to make travel between the two reasonably simple, if anything in space can be considered simple...
3. I had considered this, but even with shipping:
4. You could get telescopes on the boats, which, even if you had to spot the other planet's boats, would still be technically possible... This is probably the best idea yet, actually, if we ignore the odds of there only being habitable land on those exact halves of planets.
5. This is one of my biggest problems so far. While it would be a great way of first contact, I'm aiming for another feel. Unfortunately it's likely they would discover each other by radio if sudden visual wasn't an option.
6. They are going to be strong in different areas, and probably at least a decade off of each other in the important areas. For example, if one planet has a thicker atmosphere and/or lower gravity they will probably be better at atmospheric flight than the other world. If one world has harsher weather, they will likely be better at building things. But as far as both species being at approximately the same level of progression, even though it's improbably, I'll handwave it and call it "it had to happen somewhere."
Ahh, I forgot, it's 2018, all the good ideas are already taken... Although my idea is different enough than this that I think it will work.
Thank you all for your responses!