Good day!
Hereunder are my inputs/suggestions to address your queries:
1. AVReceivers or amps have A+B speaker outputs to offer flexibility to the consumer should he plan to use two sets of front speakers for the AVR or to use it for bi-amping a single set or to use two different speakers for HT and music as you mentioned, or to use both sets for both music and HT. Possibilities and combos are many and it would depend on your preference and liking. Try it out.
Be very cautious, however of the impedances of your speakers and the nominal load that your amp can handle. Normally, AVRs or amps are safe for 4-8ohm loads. Should you decide to run 2 speakers simultaneously, make sure that each is at least 8ohms to give your amp a safe 4ohm load for the fronts. Running low ohm loads will make your amp run hotter and eventually shut it down. After prolonged use, it will surely damage your AVR
Be forewarned also that doing so, you will eventually be able to compare different speakers and know their different signatures with the ability to do side by side tests. More importantly you will now be able to identify characteristics that you like and dislike, and distinguish your sound that will initially be your reference in auditioning other gear. Do the same for a different amp and it shall be your entry to the never ending quest of your sonic nirvana.
2. I suggest you put 25 centavo coins between the spikes and your floor and test it also without spikes. If you do not hear any difference, who cares?
To me floor mats dont look good. It's too Nova Villa to me
but if you want them, it's your choice
3. Tidying up the wires is good. Just make sure that it is looped and you dont fold it at the ends to damage it. Also, avoid joining signal cables (RCA.Component,etc) with power cables to prevent unwanted noise that may go into the signal path
4. I dont. Reception isnt that good in my area
5. Sorry, I am not familiar with your AVR but normally it is the arrow and/or +/- buttons. Press SET UP and use the arrows to toggle from different settings. I am sure your manual can guide you best
6. HF=High freq (tweeters), LF=Low freq (mids/low). You can route Speaker A to HF and Speaker B to LF
Please refer to your speaker manual first and disconnect the jumper before doing this.
Hope this helps