> We never funded the fee pool and yet the network pays tx fees in BTSFCX, where does the BTS come from when we pay tx fees with BTSFCX ?
When you register an asset, 50% of the fee goes into the fee pool. So you should have started off with 2,500 BTS in the pool.
> How can we choose to pay tx fees with BTS by default ? Disabling "Charge Market Fee" ?
I'm not sure if the GUI wallet supports this yet. It will soon iirc. "Charge market fee" only deals with trades, not xfers.
> What is the "Pool Balance" ? Why does his value is 234 578 127 ?
GUI bug, the decimal point is missing. It's in BTS (which has a precision of 5) so Pool Balance is actually 2,345.78127 BTS
> What is "Unclaimed Issuer Income" ? Why does his value is 15 421 874 ?
This value is also missing the decimal point. It's measured in BTSFCX (precision = 4) so the value is in fact 1,542.1874 BTSFCX