Can't help with the first question, but the second one is easy to answer.
Right now freqs higher than 20 Mhz are going to be iffy, depending on propagation. We are going into the winter months, and usually that's not the best time to be going that high. That's why a lot of broadcasters step down in frequency during this period. Of course if we get a flux level that's nice and high, that does help those higher freqs for a few days. But I think you'll find that there really isn't all that much above 20 Mhz in the broadcast world right now.
In general (again this has a great deal to do with propagation) during the winter during the day, you should likely stay below 18 Mhz or so, As you say at night, the lower freqs - below 10 Mhz or so - are your best bet. These lower freqs won't propagate very well during the day due to the D layer of the ionosphere absorbing the signal.
You should spend some time learning about propagation, and how it's effects due to the season and what is happening on the sun makes a great deal of difference in what you hear and how well. This site (from our HF propagation wiki) is a good place to start...
Propagation Primer - Flash Movie by AE4RV
Note that you will need Flash to be turned on to use this site...Mike