I have been in a complete hellstew of computer and software woes lately and am almost out of wits. So many problems that I have to think I have some hardware issue or something fundamental (the dreaded Fusion drive perhaps) very broken with my computer. 

Here are the list of fun things I have been going through over the last couple months.

• Time Machine has been super flaky lately. Now it has come to a point where it does a complete backup each and every time. All 3 TB of it. Kills me.
• I use two separate disks for Time Machine. One is a 6TB USB drive and another is a shared folder on a Synology NAS. TM backs up 3TB to the USB drive in about a day. But it takes over a week to do 3TB of backup to the NAS. Kills me every time. 
• Lightroom crashes almost every day, typically under heavy load and when I happen to be editing aggressively - like too many local adjustments or if I use the keyboard or mouse too fast. And once it crashes  I cannot relaunch it unless I restart the entire computer. 
• Oh, and I cannot restart easily because it is always in the middle of a Time Machine backup. If I restart then the Time Machine backup restarts as well - all 3TB of it. Kills me again. 
• Oh, and I actually cannot restart my iMac or Sierra OS because it actually never restarts. It tries to but after letting it grind for a few hours - I have realized that I just need to hard boot it by using the power button. Only way the iMac restarts. No software restarts for me. For months now - probably ever since I installed Sierra.
• And then there is Photos for Mac. The shitty photos catalogue that I keep using for legacy reasons to store my final images (Lightroom for capture and post-processing and Photos as the catalogue for final images). I used to be able to export directly from Lightroom but that now crashes. So, I export to a folder and import manually from within Photos. After installing Sierra 10.12.2 update, import often hangs Photos. Then I Force Quit and then it won't start until I restart the whole damn computer - and I cannot - because Time Machine and because iMac. 
• Oh, and another thing - I have an OWC Thunderbolt enclosure running SSDs - the Mac has never recognized it on start. Unless I unplug the thunderbolt cable briefly and plug-it right back in. And that kills dropbox. It goes absolutely crazy. I have it running on an external drive. Very bad, it seems. 

Why am I still bothering with the Apple ecosystem? I don't quite know. 

This is my 2nd iMac in the last two years. Both have been extremely unreliable. First one didn't have a Fusion drive and not sure what was wrong with it but it kept crashing - with a Mac equivalent of blue-screen-of-death. This one has a fusion drive which I've already had rebuilt at the Apple Store twice. I have Apple memory so it cannot be that. 

HELP!