Gar, as new member here, and in the same DTE district as you, I'll offer up a few pointers and experience with their planners, and some about phase converters.
First thing is zoning of the proposed new location.
Residential only, is a complete non starter for a 3Φ service. Several planners have told me, 3Φ on residential is against the public service commission rules. I never looked up the rules myself, but this is what the planners go by. If your in an area that is zoned for residential and light commercial on the same lot, that makes the provider rules different.
As an example at one site years ago, we had a commercial building with a new tenant, on frontage of 8 Mile Rd. The building was on a corner lot, of a residential side street. The customer had a fair amount of 3Φ equipment they needed to run, and the building had a 3Φ 4W Service installed. 400A with a CT cabinet. After the equipment was installed and connected to the service, it was found that the high leg was not connected at the service point. The building service hi leg wire was existing, at the service connection point, but was not terminated to the drop, curled up and isolated. A quick look across the residential side road, revealed that the 3Φ primary was existing, but the pot for the open delta configuration was missing.
The first planner had a look, and claimed unequvically that service commission rules prohibit 3Φ lines from crossing residential streets. We pleaded the customers case, but he wouldn't hear of it, at any cost. A few weeks later we tried again. The 2nd attempt got us a 2nd planner, 1st one was on vacation. After pleading the case again, he agreed to connect us and set the pot for about $1600 if memory serves correctly. He told me that the hard liner was gone for a week, and if he got the order in, before he returned, it would not get canceled. I had the customer hi tail the check over to his office, and it was a done deal. So if you have any contacts with people in the district, talk it up privately to see if you can get a reasonable planner that serves the district your in.
I have found on multiple occasions that if you gave a load schedule prepared on their forms, ahead of time, before you contact them, helps them a great deal on seeing the load you want to connect. It can help, if you pad the load schedule a small bit for future loads, don't go way overboard here. List the loads as current or future. One planner allowed me to install an 800A service on one of their 400A rated banks that was existing. Having the load schedule with descriptions of the load types and duty cycles can help greatly on getting what you need, but its on you to PROVE it, not just state that you need it. Their internal standard for transformer bank sizing is way different than the NEC values, so focus on the load and use types, not the transformer size you want.
Next thing is to have a copy of a higher than average invoice, for the existing shop location. This gives them the account number, so that they can easily look up the existing demand, and compare to your load schedule. In your case, invoices for all 3 meters you have at the shop location. I would also include one for the house meter as well, since that will need to be added to the requested service.
Proof of the existing monthly spend with them matters a great deal, in my experience. It's been all over the map in my experience. Customers with a large monthly spend, normally get what they want, with little hassle, and for very low to no cost. They see the payback period, and calculate accordingly.
On the other hand is the customer, that is a new customer, that wants a big service for something he plans to do, but has zero history with the company. This is a sure fire way to get the most denials and the largest costs, meaning all costs upfront, and no amortization factoring, for no history. They don't want to be caught holding the bag, if and when your plan goes flat.
On to phase converters. I would suggest that if you run decent size CNC's that you consider dedicated converters sized for each CNC machine.
Some are more sensitive to disturbances and unequal voltages than others. Some RPC manufacturers will suggest this as well. Then a smaller converter to run the remainder of the shop equipment.
An overly large converter will normally be factory balanced at its full load rating. When lightly loaded, the hi leg voltage will be excessive for smaller loads and lead to current imbalance and overheating. Most manufacturers have a minimum motor size listed for each converter model to help prevent this situation. Sharp voltage fluctuation from a hard starting compressor cycling on and off can play havoc with a sensitive CNC or other load. One RPC builder that I like his write-up on can be found
HERE
Be sure to check the links at the top of the page as well, he covers the material pretty well.
Paralleling RPC units is no problem even of different sizes or makes, you can even have one self starting unit, and the other compensated idlers, start from the first one as needed. As you stated earlier, two of the lines are common to all idlers, the only thing that needs to be done is check the phase rotation of each additional unit that you bring online so that they match. Swap the supply lines as necessary and leave the wild leg common to all units.
