SSD for my desktop

I am looking for advice to replace an old HDD for a SSD (256 GB max, for OS only)

My computer is a Desktop XPS 430. Year; 2009.

I am not sure if the motherboard supports SATA3. I don´t think so. I Cannot find information about it, only this info about the model; South BridgeIntel 82801IR ICH9R

Doubts I have:

1- The Deskop has an eSATA port on the back. I am not sure if performace is the same or worse than using the SATA ports inside the box.

Any ideas of using eSATA ports?

2- SSDs are SATA3 mainly these days but I am not sure if it is worth to search for a SATA2 which probably will give same performace if SATA3 is not supported.

3- Any info on SSD and controller most welcome.

Thanks in advance!