Hiho,
I have a similar set-up. All the things that you want from your soundcard are very reasonable and any half decent card should be able to handle those jobs without any problem.

As far as triggering your sampler goes, you simply send a midi out cable from your computer soundcard into the back of your sampler. Then you have a standard lead (like the ones you'd use for a guitar or keyboard) going from the audio output of your sampler into the back of your soundcard. On cubase you simply hit play and record and that's it- the tune will get played, the midi info will get sent to your sampler, the sample will play some sounds and the audio out from your sampler will go to into the back of your soundcard.

The same applies for your synths and keyboards. VST instruments also won't be a problem.

And finally a word about latency. Just remember, you don't need to rob a bank to be able to afford a card with negligable latency. The difference between 7ms and 9ms is hardly worth worrying about and with a semi decent card you'll be able to trigger VSTi's live without any problems at all.

As far the golden question of which card?

Well... I'm not in the business of advertising for anyone, but the card I've got cost £180 and I by now there are probably some cards which are even cheaper and which to an equally good job.

Stay cool