Basic Mixer questions

Hello, I'm new to RF design, I just have a couple of basic questions that need to be answered!

1 - Do IQ Mixers generally work better with higher or lower RF and LOs ? By this I mean which will work better: Option 1 where RF=LO= 70MHz, or Option 2 where RF=LO=2GHz ?

2- Does downconverting work better if the frequencies are close or far apart ?
i.e. Option 1 where RF=20GHz LO =21GHz or Option 2 where RF=20GHz, LO = 20.1GHz ?

3- On the other hand, when upconverting, is it better to have a frequency close or far apart from you source ? (if you don't care about the output freq)
i.e. Option 1 where LO=20 GHz IF=1GHz or Option 2 where LO = 20 GHz IF = 0.1GHz

4- Finally, what type of oscillator is generally better, in terms of stability, cost, output power:
A 2GHz LO or a 200 MHz LO ?


Thanks for the help!

S.