No one here can address your concerns.
El Capitan will work and will boot and work and is supported with 4 GB, but it'll be running applications that need more memory than you have available here at the speed of your local hard disk or SSD storage.
Google Chrome consumes a very large amount of memory and — if you're particularly fond of that browser — I might even price out the difference between the 8 GB upgrade and going to 16 GB.
If you are always busy-busy-busy, you could consider whether you want to learn how to upgrade the Mac yourself, and then order the memory upgrade. There are instructions on how to do this posted around the 'net.
Your MacBook Pro (MacBookPro8,1, 13", Late 2011) accepts two 204-pin PC-10600 (1333 MHz) DDR3 SO-DIMM memory sticks, and is one of the last models that is upgradeable. Apple offered memory upgrades to 8 GB and third-party vendors offer upgrades to 16 GB, per MacTracker.