Don't know about UK working frequencies, but ships will generally not be equipped with aviation VHF (they have no need for it on a daily basis), so 121.5 is probably out.
Static discharge is real. Depending upon the conductivity of the hi-line and weather conditions, allowing the line to touch the deck may not be sufficient to discharge static, but do allow it to touch before handling it.
Using a grounding wand or allowing the rescue device itself to touch the deck before handling is standard in the U.S. regardless of whether a line is used.
In the U.S., Ch. 16 is a distress and hailing frequency. Standard practice is to hail on 16 and then switch to a working channel once two-way is established. I gather (but may be mistaken) that practice is similar in Europe.
Direction of ship movement is going to depend (as crab states) upon sea state, wind, and other factors. One factor he didn't mention is seaway. The vessel may be constrained by a channel or other vessel traffic, so may be unable to take up the heading the helicopter might otherwise prefer. Going to a DIW (dead in the water) vessel is generally unpleasant.
crab's mention of hi-line techniques correlate with my experience as well. There is usually more than one way to carry out an operation. The key is to not choose the most risky way.