HI Jazz Monkey.
After two weeks of going through this lark myself I can give you the answers in a nutshell.
1) Only consider split units (as you already are)
2) Only consider top quality units like Daiken.
3) Go for the inverter models where as the set temperature is reached the whole system throttles back.
4) Only way to get cold air to flow from one room to another is to blow it with a fan. This is not as stupid as it sounds in fact as it allows one room to be chilled to perfection and another to be a lot warmer. Ultimately it's a hell of a lot cheaper than units in each and every room.
5) look at units with at least 3.5 Kwatt (12000 Btu's)of cooling ability if you are going to cool one room and try to blow some of this cold air into another room using a fan. A 9000 Btu unit has not got enough muscle.
6) Consider a ceiling mounted cassette unit (like the shops) at the top of the landing if you want overall cooling/heating. I have just had one put in the media room (5 Kwatt) and it is brilliant. Be warned though, it is not silent, none of them are!!
In a nutshell, I had to return a pair of split units purchased from Macro because they were old/cheap technology with Grade D efficiency. The racket made by the condenser compressers travelled right through the walls and across the house.

The new Daiken units installed immediately after are Grade A efficiency and the outdoor units are whisper quiet even running full chat!!!
Hope this helps, Gerald.