Hardiplank

Some of these questions were covered on some older post. I am wanting to be sure they are still current.

Is urethane caulk still the caulk of choice and any particular brand?
What is the definition of moderate contact in reference to ends of lap planks?
Still 1/8" between planks and hardietrim corners?
Does it matter if nails are wire or plastic collated?

Found these for a good price: 15 Degree Wire Collated Siding Nails. AISI Grade 304 tainless Steel.Ring Shank. .093" Wire Size.
.234" Head Diameter, Waffle Texture.300 Nails/Coil, 12 Coils/Box. 3,600 Nails/Box. On the bottom piece of horizontal window trim, how much of a gap should there be between the siding top edge and the trim lower edge (which will be hardie trim) and do you flash this? Just a note I live on the east coast of Fl and will be face nailing due to high winds and blowing rains.