I've heard bad things about the BiOrb, but I don't know what.
I'm assuming the price is okay for you, then? Bettas cannot live with goldfish. IMO the temperature is one of the main issues, and its possible for some hostiliity between the two, maybe?
I heard java fern is plain indestructible, haha. I would recommend getting it, with basic reseaerch.
I don't know how it's cycled. How are they selling it to you? Is it still filled with water, or is the gravel / filter cartridge still wet? I would be uncomfortable, but definitely ask them how they cycled it, and how they intend to keep it cycled (the beneficial bactera can die if exposed to air, run under tap water, with other various measures).
b) Again, I've heard bad things about the BiOrb, and spherical tanks, but not sure what. Just thought I'd tell you. Size-wise, it's nice ;)
c) Again, I hear java fern is about indestructible. Just the utmost basic care should be known (how not to kill it).