right then...
To hide the battery in the boot is quite straight forward - u'd have to lengthen the wiring to the battery terminals and yes you can run the power cables inside the car.
to hide the wiring loom there are different ways to go about it. I have seen some where the loom comes through a hole in the floor and up underneith and around the engine into the bay and all tired to the engine/accessories and wrapped in black tape or plastic sheilding so as to conceal it.
Others i have seen have had the loom lengthened so that it can be passed through the chassis legs. For example on mine i have run the wiring loom through the bulkhead as standard (it sits just below the brake servo) then through a hole in the chassis leg underneith the air box and back out the front where the bumper slides into the chassis and then along the front of the slam panel behind the radiator. that way most of the lighting loom is hidden away. As for the engine components wiring which is routed across the top of the scuttle around the back of the coil an down along the chassis leg some of this has been moved under the scuttle, some then loops down the back of the bulkhead into the chassis leg out the side over the gearbox and to the engine. If/When i redo it i want to run the wiring right through the chassis leg on the passenger side to the the front of the car and have the loom tightly attached to the engine thus hiding them a bit more.
When it comes to relocating washer bottle you can chuck that in the boot and run a extended wire to the pump and use the existing washer pipe that is meant for the rear wiper to then function as your front washer route.
When people hide the expansion bottle what they tend to do is use a radiator with a expansion tank attached to the side of it and have a rad that has a top fill cap on it.
To hide/remove the servo/master cylinder you can get brake pedal set ups that have remote resevoir and only require a small bottle of fluid which can be located under the scuttle panel in/around the area where the ECU currrently lives. Speaking of which some people relocate the ECU inside the car eg in the gloove box or under the dash.
i suppose since you are doing a 1.4 -> VR conversion literally none of the wiring in the bay is needed plus you will have the subframe and brake servo etc all out so you will have good access!!!
so you really are in a position to start with empty bay and plan your rewiring carefully, i would suggest stockpiling a few spare connectors as you will likely break a few. Are you going to be making a project diary?
dave