I swap my sim between my 6 plus and S7 edge all of he time. Used my 6 plus all last week, switched back to my S7 Edge yesterday morning.
I don't pay extra for iCloud... and I try to not sync with iCloud as much as possible. Since I share theme mods to the jailbreaking community, I use MediaFire to share my uploads, and I use it as my cloud to backup my camera photo/videos between my iPhone and S7 Edge. Both phones can be set to upload to mediafire automatically. I use Google contacts to sync between both.
iMessage... The thing I have to remember when switching from my 6 plus to my S7, is to deregister my phone number from iMessage. Not hard to do. If I don't do deregister my number, people who iMessage me continue to go to my iPhone instead of my S7 Edge. Most of my family and friends don't mind me switching back and forth, since most have unlimited text anyway. However, I have hangouts and whatsapp as an option... especially for my international friends that still pay for texting.
As for FaceTime, I don't use it much. Only people I FaceTime are my wife and kids when I travel. I can still face time them with my iPhone, but we can do the same with hangouts if we really need to video chat.
Now that streaming content is the norm for me (UDP helps), I don't purchase/download movie or music anymore. Some carriers even let you stream some services without counting against your data usage. Downloading movies and music is a waste of storage space for me now.
Most of the apps I use regularly are on both phones. Majority of them are free... but I don't mind paying a few bucks for an app. As a developer, I'll support developers for their work on both devices.
It wasn't difficult for me to own 2 phones on different platformsI. try to distance myself from the Apple ecosystem so I can enjoy both devices equally. However, I still use "Apple Music" on both.