2) Engage Cable. I believe this is a must. I get my cables for $22-$25 a drop. I view this as part of the cost of going with Enphase. The thing to note is you will void a product's UL listing if you do not use it in the manner in which the manufacturer prescribes.
4) Cable Management....Hard to see why you'd want to save $10 on a $10,000 bill.
I probably agree with Engage cables for the m215s. Where I was suggesting EMT and j-boxes was perhaps a special case. But one that comes up when you're not starting from a clean sheet.
I have expanded my system twice. The initial system was 2.8kW and a centralized inverter. I have a tile roof so, to help future proof, I re-roofed and added enough racking to double my array down the road when PV prices dropped. 18mos later I found 4 blem Sanyo panels and 2 m380 Enphase very cheap.
The panels had to be on a far corner of the roof away from the service panel so I ran EMT to a box near the panels' edge. Then I looked for Engage trunk cables for m380s. No dice. The m380s had been EOL'd (hence they were so cheap!!).
The 2 Engage cables I finally found were $95.
My thought process for using EMT was like this: Geez, I've got exterior EMT and boxes all over my property and there's been no issues for decades. I'm using these $95 cables to run <3.5 Amps of AC ~ 10 ft to the junction box where the fancy Engage end is going to get cut off (UL violation?) and spliced in the j-box. Who really knows how
long this cable (that looks no better than a high-end extension cable) will last on my roof.
So, that was where my question arose. I bit the bullet and paid the $95. I've since installed some m215s and yeah, those cables aren't bad price-wise. I've have no sense that they'll outlast properly installed EMT and boxes though.
As for UL or warranty violations, funny you should ask. One half of one of my m380s failed the first week. It was a thermal issue.
Enphase said no problem to replace. I confessed to them that I had modified the unit by replacing the DC connectors with MC4s to match my panels. Not an issue they said and replaced the inverter within 2-days. All's been well since.
Lastly, I agree about not cutting corners, for the above example I was questioning the value of the Engage. Furthermore, I inspect my system closely once per year as added insurance and upgraded to WEEB clips after those became standard. Loosened panel fasteners has been my only issue.