Subpanel/Isolation Transformer/Dedicated Lines

I know this may seem like deja vu all over again, but we’ve finally relocated to Texas (from New York) and will be having an electrical contractor visit in the next week or so to begin plotting out the electrical plans for the "new" house (which is actually an 1880’s house that has been thoroughly restored, including all new mechanicals/infrastructure). I am still planning on building a separate outbuilding for the music system and record collection, but in the interim, I plan to install the system on the second floor of the house.
The house has 200 amps of service, all equipment is circa 2004. I would like to have the electrician install a separate sub panel for the system-- probably Square D (I used this box the last time in NY, but will specify a copper bus bar). The question relates to how a free standing isolation transformer gets wired in. (Caveat: I will make sure the electrician I use is knowledgeable in code compliance here so my questions are not a substitute for that but meant to enhance my understanding and discussion- the local electrical inspectors are accessible and informative too, and I will get anything we do, now or in the future, permitted). First:
Location of Sub panel and Isolation Transformer-
Unlike the East, where the service terminates and main panel are located in the basement, there is no basement here, but a pier and beam with the main panel mounted to the outside of the house. (In all the houses of this type I’ve seen here, nobody seems to lock these boxes- seems kind of obvious to do so). So, I’m thinking the sub panel ought to go in a closet on the second floor, in a room removed from the listening room. I don’t know if it is permissible to locate the isolation transformer there- I’m not talking about a "black box" with a plug, but a large --7kVa or 10kVa transformer hard wired to isolate the lines attached to the sub panel from the rest of the household electrical. I gather in reading an earlier thread here, that paralleling the windings on the transformer rather than wiring in series is necessary to get the full capacity of the transformer.
Multiple Dedicated Lines-
This set up would power several dedicated lines for my audio only system which would be located in a large open space on the second floor. I learned from past experience that bundling the in wall/in conduit electrical cable was bad- electrical noise from my air compressor motor would transmit across the cabling. So, each line would be separated and run to hospital grade 20 amp outlets. (I used Porter Ports in the past- thanks, Albert! and am not inclined to buy the high priced outlets for now, since this is an interim set up). The air compressor is always an issue- it pulls some juice and has mechanical as well as electrical noise when in operation. I’m currently thinking of locating it in the same closet as the sub panel. I am assuming that if the dedicated lines are run separately, and not bundled, I won’t have the electrical interference I experienced in the last system which was only solved by using a stand-alone isolation transformer--’black box’ type for medical purposes--just for the air compressor. I still have a couple of these, but it seems like stacking one isolation transformer on another is just wrong, and ought to be unnecessary, i.e. using a medical grade smaller "black box" transformer for the air compressor that would be plugged into a dedicated line/receptacle from the sub panel that is already isolated by the bigger transformer for the sub panel mentioned above.
I still have to figure out the best layout for the receptacles, and also need to get a line downstairs, to the front parlor, where I will have a second "vintage" system installed. (That system is worthy of a second thread- I got my old Quads restored and will be using some fun pieces in that system, all from back in the day. That system will remain in the main house, even after I build the outbuilding and move the main system there). It seems a little crazy to feed this first floor small system from the second floor sub panel I’m contemplating, but the alternative is to feed the downstairs "parlor" system directly from the main panel. I haven’t figured this out yet-- I would like that to be isolated by a transformer and run from dedicated lines- but this would probably mean feeding the ’parlor system’ from the main panel via ancillaries that would be mounted to the outside of the house, or in the large crawl space beneath the house-- not as good as air conditioned closet space on the second floor closet for the main system. Plus I have no idea how one would install an isolation transformer that is in effect outside of the air conditioned space of the house interior--seems like that would pose code problems as well as heat, rodent and other issues-ugh!

As mentioned, much of this work would be for an interim set up until my outbuilding is approved and constructed. Apparently, I can get separate service to the planned outbuilding (yay!). but even though main house set up I’m currently comtemplating is a stop gap, I want to do it right. Jea48 has been enormously helpful on some of these questions in the past, as have a few others, including Almarg.

I’m pretty excited to get all this moving--the house is gorgeous, and located right in town (which has great benefits in terms of walking to things, but it is quite dense, as is typical of an urban neighborhood, with apartment buildings and the like, nearby).

Any input from the denizens and wizards of electrical would be greatly appreciated.

bill hart