I was originally going from Ljubljana but see that the IC211 at 14:11 actually travels through the capital leaving at 14:45. Do I have to buy two tickets? i.e. Kranj to Ljubljana and Ljubljana to Zagreb
It is possible to travel either with two separate tickets (Slovenian domestic Kranj-Ljubljana for 4.38 euro & international Ljubljana-Zagreb for 16,4 euro) or one international ticket Kranj-Ljubljana which should cost about 21 euro. As you can see, in terms of money it's not a big difference. You might save some money only if you go for option c - purchase domestic ticket Kranj-Dobova (last Slovenian station before the border) for 11,36 euro and international Dobova-Zagreb which should be a bit less than 5 euro, thus making it in total about 16 euro for the entire trip Kranj-Zagreb (instead of about 21 euro with options a & b)
... as the website doesn’t show a through train from Kranj.
Hmm? Which website and what date? Since train #211 is Villach-Ljubljana-Zagreb-Vinkovci, it goes through Kranj and stops there
Can I buy tickets, in advance, from Ljubljana station or should I buy them on the day at Kranj?
Whichever convenient to you, both options will work. In advance purchase in this case doesn't really save you anything, since discounted tickets aren't available for this connection, but purchase in Ljubljana might be a bit easier (first of all due to language factor) then buying the same ticket at some smaller stations.
I’ve also read so many different opinions re bus vs train travel from Zagreb to Split. My itinerary there is a bit of a disaster so we end up with return travel from Zagreb to Split spending a few days in each. But no matter. The bus is cheap and frequent with convenient times. The train longer but less frequent fast journeys. I reckon that by the time I’ve factored getting to & from the airports and waiting around, the bus takes not much longer with more convenient times. The other option is one way car hire - but perhaps I’ve read too many disaster car hire stories there. Anyway I’m happy to try different modes of transport each way. Your thoughts?
Well, on this website we usually suggest rail options
But it doesn't mean that we didn't try bus. When I did a bus journey myself I specifically choose the bus which travels by the sea coast (it has longer travel time of about 8 hours) and not the one which takes faster highway route (here buses make the trip in about 5 hours), since it seemed to be way more interesting. Car hire will allow not only to see those nice town along the coast, but stop whenever you like + make detours (e.g. already discussed Plitvice lakes)