You can use Adobe Lightroom mobile version, available in both android and ios devices. You can also use picsart mobile editing app but I recommed using adobe lightroom for mobile. Both of them are free in mobile and I really don't know any desktop free editing software for photos but if you want to edit video you should use Davinci Resolve 16 it is the best free professional video editing software for desktop there are many professionals who use Davinci Resolve.

There are times when using an adapter may cause lag in camera functions such as your cameras autofocus system. It will work better with the native lens but it is not always true there are adapters which are very great and will do the job. My suggestion would be if you will be upgrading in sony only then native lenses are the best choice for you if not the best choice is to buy the best adapter you can find. By reading what you are asking I am assuming you wont be buying an ef mount camera from canon so the best thing to do is buy native lens.