anti aliasing seems to drain fps in modern games..so my question is do I really need anti aliasing at 1080p for a small monitor like my 21.5" Asus VX229H monitor?
You can use FXAA/MLAA/SMAA for cheap AA option that virtually removes all aliasing for 1 FPS drop. I've been using it since Nvidia/AMD introduced them in 2011 or so.
It's up to you. I usually keep MSAA on 2X or 4X depending on how the game runs. Sometimes I just use FXAA which seems to do a pretty good job. I also have a 21.5 Asus monitor. I have the VE228H. I also play games on my 42 inch TV sometimes.