Adrian,
The roughing gouge will depend upon what you're intending to turn down from square to cylinder - I like to use a fairly large one, suitable for table legs, lamp standards, etc. and I've become quite adept at using it on smaller projects too. Probably, a 3/4" is the place to start.
Parting tools also depend upon what you're parting from what. I've got a couple of different sizes, but I favour the very thin variety for fine parting off - although you can get the occasional grab with them if not careful. Larger parting tools can double as small skews - but only if very sharp!
Spindle gouges are much of a muchness (as my dear old Mum used to say!), the 1/2" is pretty well standard here. If you only do occasional spindle work, have a look at the Spindlemaster, it's a little more user-friendly.
Skews are an acquired taste. I've tried the oval ones - hated them and reverted to the largest flat one I could find. Remember to get the tool rest above centre and never try to plane inwards from an edge, otherwise you're likely to get a spectacular dig-in.
Bowl gouges come in a variety of sizes, although the 3/8" is the most often used. I do have larger and smaller sizes, but find that the 3/8" is the one I most often reach for.
Round nose scrapers are not my favourite tool, but around 1" is readily-available and fairly user-friendly. HTH, although I'm sure that there will be other replies that will differ - turning swiftly becomes a matter of personal preference and I'm pleased to see that you've got your eye on quality right from the start.
Ray.