Firstly, what does your system currently exist of? Solar panel wattage, Battery management system , battery type and size?

When you say your consultant wants to replace everything, what components has he specified to be installed?  At what cost?

What is the wattage of the largest appliance that you propose to use or a combination of two appliances? 

To answer your questions.

a)  Solar cables can be run internally or externally in cable conduits.  Internally preferably using cupboards where possible.

b)  It can but when you say power system do you mean battery, solar charge controller, 240v charger, DC to DC charger and inverter?

c)  It is possible to run a cable with an RVD installed from an inverter to the caravan 240V inlet.  I and many other do it this way.

d) Possibly but it depends on the proposed use. Generally you would run the site power to your caravan 240V inlet.  Then look at a way of providing power to your power station if for instance it consisted of a 240V charger.

d). Sometimes a reasonable cost and sometimes an arm and a leg.  It is just a matter of who sees you coming and Im serious on that.  A system is not costed on the size of the inverter as that is just one component.

Peter has asked what you power consumption is, that being what you propose to use and for how long per day.

Sometimes a portable power station is the best solution for some people and even a portable solar panel where it is difficult to put solar on the roof or they can be used as a supplement to the system.  Flexible solar panels may be the best option for you if you want solar on the roof as they are fairly lightweight.

https://www.solar4rvs.com.au/solar-panels/flexible/

Tim