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!

Would depend on existing roof structure. It would be quite difficult to do if it has a truss roof as you'd be cutting the bottom chord.... Not ideal as the truss is an engineered member that relies on the parts working together. If its a conventional cut roof then there is the possibility of doing it. Still a bit of roof framing work beforehand before cutting the ceiling joists. Personally you'd have to be pretty keen for the higher ceiling due to cost which no doubt could make it uneconomical, although it could look pretty good once done. As noted get it checked and estimated first. $250 per room is nowhere near the required amount....I'd expect another zero on that figure....

answering your questions: change the sliding door to a bench height sliding window and use the salvaged sliding door in the western end of the dining room where the best entry position is for the deck, you MUST have a proper legal drains do not consider anything else...the drain pipe for the garage laundry can be on top of the concrete floor, behind the washing machine and through the sink cabinet and/or under built in storage and only needs a few cms not a whole floor and no stepped up area that you would see or trip over.. the laundry can't be in a separate room as there's not enough space for a separate laundry without compromising the size of the garage...a laundry cupboard 80 cm deep is enough for the washing machine (allowing for the drainage pipe) you could use the old line cupboard to store anything you want but it's not cost effective to change, the entry foyer is already as big as in many modern homes and there's generous flatpac biw space in the small study.... the family bathroom is 2380 x 2370 (ie the old study minus 1m for hall way and wall thickness and, arranged exactly as shown to allow for the wide window there should be space for a bath up to 1800 x 750, vanity about 1200 x 500 and shower space 1200 x 800 and leftover space makes the small linen cupboard with the door deliberately opening towards the shower to use the back of the door for hanging racks for towels and clothes....btw i understood your priority was maximizing separate sleeping rooms and minimising costs...my last plan has five separate sleeping rooms plus the lounge with sofa bed totalling sleeping places for at least 10 people plus the potential for bunks in the garage so you need to decide what is most important and where you're prepared to compromise

How long is a piece of string ? You are renovating . Is it period correct , or updated ? is it 'workers' style still or are you going luxe ? Me , I'd probably go for something rattan and gold but that mightn't suit your style . But as Kate says , is there enough height ? I just googled , and you can get a round slim 'thing' that has an LED ring of lights around the outside , and looks like 30 or 40 'knive blades' that rotates , says it is 11 cm height , but it looks 'different' ( like say a UFO ! ) so may not suit your style , and each knife blade is only 40-50mm wide , so how effective it is I'd have no idea .