OS X installation on separate HDD (and windows on another)

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I have Dell XPS L501x laptop, currently running Mavericks. I will be upgrading to Yosemite (will use Clover) and also doing some system upgrades. Since my laptop is old (2010), it has BIOS (and no UEFI support)

My current config: i7 740 (first gen Intel proccy), 4GB RAM, 500GB SATA HDD, nvdia 435m graphics card.

- I want to replace HDD with SSD (Samsung Pro 840, 256GB)

- Remove optical drive. Add the HDD here with the caddy

- Replace RAMs with 2x4GB

I need multiboot system. Currently both OS X and Windows are installed on same HDD. Now I am thinking to install OS X on SSD, Windows on HDD. Is that the right way/suggested way to do it? OR shall I install both on SSD? I often read that it's better to install different OS on different partitions, but why so?

Secondly, can anyone give me some instructions or point me to relevant guide? I am not asking for entire tutorial, just brief points will do. Thank you