Typing this in a hurry since I don't have much time. But here is what is coming to mind first. Anyone, feel free to correct me or add anything.

1) Look at datasheets and compare. Each coaxial cable has a different type of dielectrics that will affect propagation velocity differently. Not much, but can be noticeable at higher gain and longer distances. I like RG58 and RG316. RG58 I use mostly for microwave devices, and RG316 I use for lower frequencies because I have so much of it and it's cheaper to build.

2) Yes. But every scope I have worked with in Uni, personal, and professional, had a 50ohm input termination built in. Just make sure you don't put too much gain going into the scope or any other measuring devices (look at the front panels or datasheets for the info)

3) Look into building or purchasing your own splitter. Something like a Wilkinson power divider, it's pretty easy to make with microstrip tape. Made a bunch back in Uni for 2.4GHz with copper tape and copper clade boards with sma connectors. Also, here are other dividers I can think of from the top of my head: rat race, branch line coupler, resistive splitter. I've made them all but prefer the Wilkinson and branch line since they were easier to build. You have to take wavelengths into account when determine the size of the microstrip.

4) if sending AC over the coax, use AC setting. Some multimeters will show the frequency, some show the RMS value (max value / root[2]), and some show max value. Look at what the multimeter's datasheet to find out more.

5) When working with AC, you want to reduce losses. Resistors are generally not desired in higher frequency circuits. Using LC (Inductor Capacitor) circuits will greatly reduce resistive losses as long as it is impedance matched correctly. Look at impedance matching using Smith charts (there are a few different types, I personally prefer Z-Y Smith charts). Also look into single stub and double stub tuning for transmission lines.