Without knowing exactly what mac you have, it is difficult to give advice.
you can never go by problems others have while upgrading or after. You may or may not have the same problems. The thing about upgrades, is they also include the lastest security features. Macs are generally safe but only as long as it is updated.
I would suggest doing a search using el capitan problems
as keywords and you will find several articles of common problems and how to fix them.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic