Either will be fine, I personally prefer the OWC Caddy but that's just because it feels like it has better construction, apart from that they both do the same thing. I haven’t tried running Raid on this setup but I don’t see you having any issues. Let us know how it goes.
What issues are you having with the T2 Chip? As for the warranty goes, while you may be able to get away with sending the 32GB ram in with the machine but I would reinstall the 8Gb before sending it in. You can visit any apple store for the repair or just call the support number.
Seeing as a new Motherboard is like $20, id just order a new one. it isn’t worth the time to try to diagnose the no power fault on the board. DualShock 4 Controller Motherboard and Midframe Assembly (JDM-001)
Hey Matthew, Sounds like a Sensor is damaged. This causes the Computer to think its running a lot hotter than it actually is and throttles down the CPU and runs the fans high. You can use a Sensor Checking software to see what sensor it is. Sensor check software: http://www.tunabellysoftware.com/tgpro/ If it’s the trackpad sensor you will have to deal with prying out the battery carefully for replacement, otherwise its going to be a Motherboard repair, it shouldn’t be too big of a deal for any repair shop offering micro soldering. As long as they know what they are doing :P
I suspect its most likely a software issue. Go to Settings - General - Reset - Reset Network settings. You will loose any saved Wifi Networks but this may fix your issue. Also check to make sure you're fully up to date. My last step before trying hardware would be a full iTunes restore. It could be the Wifi/Bluetooth Antenna iPhone 6s Plus Wi-Fi/Bluetooth Antenna.
First, did you transfer data or install an Operating system on that drive? If you just installed the drive right out of the box nothing will show up. If you do have an OS on the Drive, Power on the laptop holding the option key. This will show you a list of Bootable devices available. If your drive doesn’t show up here then double check the Cable for any marks or damage. These are fragile and may have be damaged during install. Try installing the original HD and see if that shows up again. If it does, You may have a bad drive or the data has issues and needs a reinstall.