the ukraine in september

i'm going to spend a week in the ukraine in september and i'd like to know if booking train tickets at the station (especially in kiev) is a real pain in the ass for foreigners as i was told.

i'd also like to know if there's even a slight possibility trains to/from lvov-chernivtsi-kiev-odessa will be full if i'm buying a day-to-day ticket (in the morning for a night train)? i've been told it was quite impossible to get tickets for crimea in the summer (due to the crowds of locals going to the seaside at that time of the year) and that it was even worse in odessa.

and finally, can we get for instance a ticket chernivtsi-lvov in kiev and a return ticket?

thanks in advance for answers:)

We don't say "The Ukraine" anymore, it's just Ukraine.