It depends entirely on the specific app. Whatsapp offers its .apk on their official website. Some apps need root, which is necessary for google services to run. There's also the two account system that is used on unrootable phones such as the A7 or A5 pro editions.
You will have to do your own research for each of your most used apps. However, the good news is that many major apps do not need gapps. The biggest roadblock is usually banking apps. It's possible to use the Aurora store to bypass some of those issues, though be aware that installing paid apps is going to be a hassle.
A5 and A5C are rootable as they use snapdragons which means they can be sold directly with full Google play support. It's recommended to remove the bloatware on there however.