welcome sergio
you probably won't need too many voices, (just let your ears decide), I guess 6-8 will be sufficient because the individual voices are extremely good - and this will be no problem with CWA's synths.
With Solaris and Flexor you could build extremely complex synth structures and may in fact run low on DSP resources. A solaris voice may consist of (something like) half a dozen oscillators and filters, so a 'numerical' 10-voice poly is really a 60 voice poly effectively

Btw you made good choices of the synths - nicely comlementing each other
You might run into trouble though if you'd like to include the latest STW reverbs and FX. The Pulsar One will get in the way of PCI transfers because it has a different low level IO, it can't keep up with the 'modern' boards and as such will be the weakest link in the chain.
Your best option would be to sell the Pulsar One and get a Scope Pro, thus making 18 DSPs.
The effects above are highly recommanded, and they'll give the synths an extra sparkle, and save some voices, too. Specially the CD100 chorus delay which comes with the plate reverb can make stuff extremely thick, broad and 'expensive'
cheers, tom