Hahaha, I can't imagine a PRO would give you a hard time in this forum! It sure sounds like you've got your hands full. Gosh. I'm in the states. East Coast. In my experience for this area I've worked with a designer most recently who charged $150 per hour. We spent about 6 hours over a 2 day period where she advised & kept me out of trouble getting a color palette together. We went shopping and she helped me chose bathroom tile and plumbing fixtures, kitchen appliances. She's very efficient and we accomplished everything I needed. She billed me $500 at the end of the month and I pd her like that. I know it can get more expensive and complicated when you want them to choose fabrics, furniture etc.

Yes the last pic looks great. Cost is difficult to predict as it would depend on products used etc. Timber thats painted, aluminium, etc. Taking a stab here, say $5000+?

"As long as there is sufficient air flow for your unit it will function well", And there in lies the problem. According to that photo the OP does not have enough clearance on the porch to make an enclosure large enough to allow sufficient air flow. Even if they did enclosing the unit allows for re circulation of air that has already had it's temperature raised to cool the condenser coil. If the coils are not cooled properly the unit can't dissipate heat trapped in the refrigerant. This lowers efficiency and can damage components "it protects the unit, adds easy access for maintenance" Protects the unit from what? It is designed to be outside. Sun, wind rain snow bugs etc were all taken into consideration when these machines are designed. I never said operating costs would be unreasonable, I said efficiency would be lowered. Unless you are out there with a set of manifold gauges and are measuring performance, you have no clue how that unit is performing. Reasonable operating costs can only be quantified by the person paying the invoice. If you earn a six figure salary $1000 a month for electricity may seem "reasonable" If you earn $30k a year, not so much. . At the end of the day it's not my equipment they can do what ever they like. They can let the system breathe like it was designed to do, be cool when they want/need to be and live with the ugly box on their porch. Or they can take bad advice, risk damaging their unit, have expensive repair or replacement costs just so it can be cute. Choice is theirs.

this is a much bigger changes than just a wall and involves foundations, floor and roof as well as plans and Council Development application but the plans imply that you will be making the building smaller which is a very unusual choice but you will need to ask a builder for quotes