Maximum PC

Hi everyone,
A) I have 2 laptops (Toshiba X505-Q898) that are SATA-300; each with a 60g SSD and a 500gb 5400rpm HHD.
B) My third laptop is an HP dvnr6112 with serial ATA for the interface but the xfer mode is SATA-300. It has a 640gb 5400rpm HDD. I'm confused by this-can I use a SSD in this laptop?

I want to upgrade the 60gb SSD in each as they have quickly run out of room due to Win 7 on one and Win 8 on the other. When the usual suspects are added to the OS, the space is eaten up. My questions are, in no particular order:

1. Since the Toshiba laptops are both SATA-300, what type of SSD can I use and what size is optimal for the OS and all the other normal programs that get added (e.g., AV/Anti-spyware/Skype/Opera/etc)?

2. What SSD has the best track record for longevity/dependability/MTBF/etc?

3. Is there any point in replacing the 500gb HHDs w/ SSDs? They are used for photo storage and light gaming.

Thanks in advance for any and all advice. I enjoy replacing parts and upgrading my PCs to maintain pace with the times but SSDs are a first for me.

Best regards,
Jeff