SE 1 complete is a really good start. SE 2 complete is a really great addition. I haven't heard the choir from SE 4, but 255 is a lot to spend just for a very watered down choir especially considering the Standard Choir is 345.
A few things you should know: The SE instruments are watered down versions of the regular libraries (which contain a lot more articulations and samples). However SE gives you a good collection of articulations (especially with the plus versions) and will put a lot less strain on your computer compared to the regular libraries.
All VSL libraries (other than Synchron series) are recordered "dry" you will need to add reverb to them. Getting one or more MIRx reverbs will give you fantastic results and is very easy to use. You'll also eventually want to get VI Pro.
Finally, VSL seems to have a new sale practically every month, so if you can't afford to get everything you want in one go, you can always start with SE 1 and a MIRx, then just wait for everything else you want to go on sale.
Best of luck,
Michael