1) in Standard Premier this has always been a bit of a mystery to me as well. I was told that the allocation depends on how many there are in your group when booking, but that doesn't help me as I almost always travel alone and rarely get a solo seat unless I book 2-3 weeks out. And I have a Carte Blanche. That could explain why the "family" seats at the end of the coach (73-78?) are often not booked - perhaps they are held back for groups and not offered to solo travellers?

There is a surprising number of no-shows, though. Many times I've changed my booking at the last minute at the station and been given a "standby"-type ticket (= access to the train but a tip-up seat in the worst case scenario), and in all cases there has been a seat free. But I'd hazard a guess that no-shows are only ever around 10%.

In Standard they still seem to fill up the coach from seat 1 upwards, so if you book seat 88 you're almost certain to have the seat next to you free, unless someone has proactively chosen it (and it isn't popular since it's next to the luggage racks and the toilets).

2) I haven't encountered that one. I've often booked online at the last minute and printed the ticket at home or downloaded it to my mobile. Are you sure? It may be a legacy piece of software from the days where the choice was to have the ticket posted to you (which you couldn't do too close to the date) or collect it at the station. Either way, you should always be able to retrieve the booking at eurostar.com and print it at home.