Daniel
Great questions, a ham license is an opportunity to keep learning. Good answers here.
Best to get 50 ohm coax, but as others suggest 75 ohms will work. I have never used a balun on a dipole. You can make a center support from a scrap of PVC, as strain relief between coax and the wires is vital.
A dipole interacts with the ground and everything else around, so cutting it for 468 divided by frequency in MHz provides total length in feet, but almost always needs some adjusting. Make wire a few feet longer, and wrap the extra back around to shorten it. You will need a swr meter to adjust this, see what you can find or borrow from a nearby ham.
Be patient with the low power bitx but you can make contacts.
73 Curt
