These answers are correct as I’m writing them, on 9 August 2021. You might find there are some differences when you’re looking at the site!
a. https://www.seat61.com/Russia.htm. You can read this as “h t t p s colon forward slash forward slash w w w dot seat sixty-one dot com forward slash Russia dot h t m”. You could leave out the first part of that and just start with “w w w dot…” or even start “seat sixty-one…”.
b. More than 6. There are six main options, and then ‘other routes and options’.
c. Three whole days. Day 1: London to Berlin. Day 2: Berlin to Warsaw, then a sleeper train overnight. It arrives at 16:58 the next day.
d. He describes it as glamorous, comfortable, safe and civilised. There is a restaurant, and the option of having your own sleeper cabin.
e. There are five ways to do it, online or by phone.
f. Two sleeper trains (Warsaw to Kiev, and Kiev to Moscow).
g. and h. You’ll have to decide that for yourself! I would personally take options 2 or 3 because they look quicker and less complicated. And right now I’d fly, because all of these options are expensive and appear difficult to book – but I hope that will change in future.