At a MINIMUM, you've GOT to have / mounted, because that's your root filesystem; without that you aren't going anywhere.
Most systems will have /, swap, and /boot partitions. Some will also have /home. (That's ignoring things like /proc, /sys, /dev, which are system, which are tmpfs or some variant, like proc).
Also, filesystem type plays a role in the 'discard' option, as not all filesystems support the TRIM operation (e.g. ext2, DOS, FAT, tmpfs, proc). Ext4, BtrFS, JFS, and XFS all currently support TRIM.
I also forgot to mention that you need to have the partition aligned on an SSD block boundary. The block size varies according to manufacturer, but aligning on 1 MB boundaries seems to provide the best option, and with drive sizes being what they are, 1 MB is inconsequential.
As for RAM, 4 GB is probably fine unless you routinely have a lot of tasks open, or you run applications that use a lot of RAM.