That budget is not enough to get a decent ssd.
You can register the ssd with plextor and claim warranty from them.
I agree with you if it's 840 evo. Just get whatever you think good
Yes, just get whatever that suits your budget

liteon s900 got 8XXmb/s write speed?? 

yes you do. just refer to the mobo manual for the right location of the intel port.

i suspect you have plugged the ssd into a non-intel sata3 port, hence the slower speed.
yes. it will be your storage.

what do you wanna achieve? a dual-boot? if you wanna have a dual-boot system, it's better to review the tutorials available online (google them. there are a lot of them). if you don't need that, it's better to unplug the hdd, install windows with only ssd, then reconnect the hdd to the system after that. better yet, just clean up the os/system/recovery partitions on the hdd first to avoid boot issues if you don't know how to handle it.

Previousy i made an assumption that you only have 1x 1tb hdd that acted as boot and storage drive. Leaving old system partitions as is sometimes create messy situations to users that are not familiar with os installs. My bad