matching satellite to floorstanding speakers

Hi,

I'm planning to buy the Jamo S608 (or maybe S606) floorstanding speakers to go with Marantz SR-5007 AV Receiver amp.

The floorstanding speakers (either S606 or S608) exist as 5.0 packs but the surround speakers are bookshelf and a little too big to install on my wall. Therefore I want to buy separately two floorstandings and just two surround speakers (without a central speaker).

Question 1: Is it a problem not having a central front speaker ?

I'd like to get the Jamo A 510 satellite speakers as surround which are white and go well with my wall. Of course they haven't the same exact characteristics as the bookshelf sold with the packs.

Question 2: Do I have to chose sourrounds with the exact same characteristics as in the pack ?

Question 3: beside power matching are there other rules matching speakers between them ? I mean not everyone buys packs of 5.0/5.1/7.1/... speakers. Sure some choose each one themselves. What are just the rules to match different speakers ?
I know this is a too general question but my focus is to match floostandings and sourrounds.

thanks

Thank you commsysman !

I'll take a look at your suggestions.

In the mean time I just realized that the satellite speakers I mentioned (Jamo A 510) are 8 Ohms while my floor standing speakers (Jamo S608/606) are 6 Ohms.
Regarding sensitivity, the bookshelf speakers already in the Jamo pack have 2 or 3 dB less sensitivity (at 88 dB) than the main floor standing ones (at 90 dB). So I presume that sensitivity, even if important, doesn't necessary have to be the same but I agree with they must not be too different.

Impedance here is more an issue I think. Actually I don't know how bad is for the amp to deliver on two different sets of impedance. My amp sure accepts 6 and 8 Ohms speakers but there is no mention that it can accept them both simultaneously !