Electrical – How far is it recommended for pipework to be from electrical sockets and switches

You can but that takes some work, re-routing wires. I don't know how many breakers you are talking about, but if it's just 2 or 4 you can and you have room in your panel you can use a breaker interlock switch.

The silver bar mounted on the breaker handles does not allow both breakers to be on at the same time.

To answer your question, yes, you can use a transfer switch. But from the picture you can see the advantages of using the interlock. No extra wiring, no subpanel to install. No more breakers to buy. Not many electrical distributors will stock this, and the brand does matter. These usually don't work with breakers / panels from different brands. They are not permanent so they can be removed easily.

EDIT - This is why all information would be great to have. A xfer switch is made to move power from 1 panel to another panel. You can't switch some of the breakers of the panel. So basically the way I see it is that you will need two sub panels, 1 for one task and another for another task. Probably a couple of j-boxes to do some of the wire make-up because some of the wires won't be long enough. Lets say that totals to 30 or 50 amps (just guessing because you have not told anyone that.) Then instead of buying the more expensive xfer switch you can use the interlock, switching the breakers feeding each sub panel.

It really would help if you gave more info, like how many circuits (poles and amps) for one task and the same for the second task.

There are other items you can use for simple things, like breaker handle locks that screw on;

or breaker lock outs.

Either can be used to lock on or off. The breaker will still trip even when locked. I would prefer the one without the padlock.

You should also check local code to make sure there is no problem having the receptacles out of use, even if it is for part time.

The crawl space case

Wiring in a crawl space (wet location) can be done successfully using a variety of means:

• THWN (pretty much all building wire you buy at the borgs these days is both THHN and THWN) in either rigid metal conduit or schedule 40/80 PVC conduit
• Type UF or NMC multiconductor cables, but not ordinary NM-B, or
• Type MC cables rated for wet locations (i.e. those with an overall PVC jacket and THWN or XHHW-2 internal wires)

However, given the circumstances (i.e. the persistent wetness in the crawlspace), I'd be most comfortable with THWN in PVC and nonmetallic junction boxes down there, with the risers being THWN-in-PVC as well. The main downside, though, is that not only is this an expensive way to wire a house, most "wet location" electrical equipment will not survive being bathed in another storm surge!

Wiring in soffits

The soffit proposal is elegant; however, the main problem is going to be providing access to junction boxes -- you'll need to have blank plates interrupting the molding (preferably on the bottom of the soffit) in order to provide access to junctions:

314.29 Boxes, Conduit Bodies, and Handhole Enclosures to Be Accessible. Boxes, conduit bodies, and handhole enclosures shall be installed so that the wiring contained in them can be rendered accessible without removing any part of the building or structure or, in underground circuits, without excavating sidewalks, paving, earth, or other substance that is to be used to establish the finished grade.

Further more, you'd have to use an "old work" type of junction box in this application as you wouldn't have framing members inside the soffit to attach the boxes to. While the 3" by 3" soffit interior should be adequate for cabling, I would not use a conduit inside it due to the soffit interfering with conduit body access. I do not know of any fire code requirement for horizontal cable chases other than them requiring firestopping when they penetrate a firewall; however, as mfarver pointed out, your AHJ has the final say on that, and internal firebreaks in the chase would be wise.

Could a busway be the best way?

Another option for the soffit wiring case would be to use a plug-in, non-ventilated, totally enclosed busway system with branch circuit breakers at the outlet taps and type MC cable run exposed or NM run in surface raceways for the drops/horizontal runs to outlets and luminaires. While unusual for a residential application, plug-in busways offer a high degree of flexibility in layout, and can be subdivided so that branch circuits can be moved with only modest impacts on power to other parts of the house.

There are two drawbacks to this approach, other than it being relatively costly, though:

1. A means of access into the soffit that does not damage the soffit would need to be provided: either the soffit side panel could have hinged access panels in it, or the screw system designed so that the side panel can be removed and replaced without causing any damage to it. See NEC 368.10(B) for details.
2. You'd need to locate the branch circuit breakers at the tap-off points -- while this doesn't limit the height of the busway, as per NEC 368.17(C) and Point 1 in 240.21(A), there has to be some sort of rod, chain, or what-have-you attached to the breaker handle so that it can be operated from floor level.