You can get any colour paint you like in any strength - 1/4, 1/2, 3/4 or full - its only a colour, so they will mix it to your request. Have you made yourselves a colour board? if not, you will need to get all your selection colours together and then go to bunnings or a paint shop and get some sample pots of the colours you are debating. (yes it will cost to get sample pots, but seriously you need to do it - and get the varying strengths in the same colour as well). If you are worried about the render colour marking, go the 1/2 strength on the render and 1/4 on the mouldings. Your Wow factor will come with your varying textures - brickwork/render and trims/timber doors, and the wrought iron. I'm guessing you have exterior lighting? some beautiful exterior lights will be the icing on the cake.

Gal will go grey (mid to dark grey) over 12 - 18 months. Initially VERY bright. The energy absorbed changes accordingly, from sub 5% absorbed to ~35%. Zinc maintains brightness for longer, though still suffers some dulling. Say 5% to 15% over time. This can be avoided by coating with a product called 'Sharkhide' metal protectant, used to stop aluminium boats oxidising. For there reasons many councils will not allow zinc or gal roofing (visual amenity, reflection issues), while making the houses more prone to requiring summer aircon at the same time. Surfmist Colorbond starts around 9% absorbed. If purely for energy reasons, a light colour might be the only option. If going dark, I would suggest at least doing the 'less aesthetically important' sides and rear in a light colour. Your call. If you go all dark, ensure you have good roof space ventilation for the summer that can be closed in the winter, and lots of well installed ceiling level insulation. Spray foam is more reliable over time than batts, see Spray It Solutions or similar (they have the Formaldahyde free Canadian Icenene foam).

Like your choice of grey. Is the house well insulated? If not, you said you didn't want to sheet the ceiling rafters but it would help with cooling inside if that is an issue. I did a similar house in Mt Tambourine, replaced the first metre of timber decking that had been weather affected and then clad the underside in corrugated iron to let the water runoff but keep the ground floor verandah dry. You will have to get an engineer to check out the load bearing before you replace decking with tiles. Then the tiles will need more cleaning than a timber deck. Don't paint your brick, do all your improvements and then take stock. Painting means creating work for yourself or employing a painter. Every time I render I put an oxide in the cement, its fiddly but the results are worth it, never have to touch it again. Try to make a feature of your Front Door as it is a nondescript at the moment. Two nice pots with plants or hanging baskets either side, paint the door in a contrast colour to make it stand out. Good luck and enjoy the journey.

You never mentioned your budget that you're willing to spend. You could add a thicker fill backed insulation blanket - 50mm, 75mm or 100mm are the common thicknesses. Steep roof pitch so would need scaffolding, harnesses, etc.. which adds up quickly. Probably still not enough insulation though but probably cheapest option. Insulation under existing timber linings then reline over the top of that as some have suggested. Working at height though so would need scaffold set up again and working overhead is not fun nor easy. You could replace the roof with a sandwich panel roof. Try Versiclad or Kingspan or comparable. They have a polystyrene type of insulation between an outer metal roof sheet and a metal inner sheet. These are heat laminated together. Again different thickness available from 50mm up to 180mm is common. The 180mm has a R rating of 4.7 which is quite good. Again steep pitch, etc., probably need new ridge capping, etc.. Probably most expensive option...... Keep us all posted on your decision though!