the existing bathroom has everything that most of us want, space for a double vanity and generous mirrored wall cabinet, a double shower and a view of the garden from the toilet without having to move any plumbing!! Unless you desperately want a bathtub the existing bathroom layout is already excellent with simple removal of the dividing walls and refinishing....I agree it's often poor economy to worry about the cost of moving plumbing but in your bathroom the plumbing happens to be in the cheapest and best spot already...additional savings can be made by asking if the vanity, taps and toilet are in good enough condition to re-use, can you minimise the glass screens and do the demolition and painting yourselves and then your major expense will be the cost of new waterproofing and tiles and the biggest decision will be which tiles?

subject to precise location of windows my suggestion has the ens and bathroom with their own windows for daylight and ventilation but you'll need to post a close up view of the old bathroom, master bedroom and downstairs workshop and garage with all measurements to work out the new laundry with potential laundry chute..the two new bathrooms appear reasonable but i'd expect to spend at least $20,000 to $30,000 or more depending on new fixtures and finishes.. careful salvage and recycling of old vanity, taps, bath etc might be worthwhile but sometimes the cost of the extra labour is more than buying new and converting the laundry to an extra bathrooom and replacing tiles in the old bathroom won't be that much cheaper and the ens is the best improvement and would improve comfort for the whole family as well as potential resale value

there's not enough space to have any open shower the best option is the sliding glass doors but a shallow bench with semi recessed handbasin and mirror doored wall cabinets would feel more spacious than a vanity

your plan looks ideal although i would have a free standing shower seat rather than built in, the biggest bath leaves a small ledge on either end for standing shampoo bottles etc, a stacking glass shower door about 1400 wide (less in the way when open and less drips on the dry floor and a short wall at the end of the vanity to avoid the hard to reach gap) the width of the bath/ shower space should allow for an 800 wide bath, 900 wide shower long enough to have a towel rails within easy reach and mostly out of shower spray...fine details like teh shoer grate and floor slope will need to be confirmed by a plumber but rearranging new toilet pipes (inside extra deep new wall cladding?) will make a much more spacious bathroom with option for an extra wide or double vanity and consider wall hung toilet and vanity for the most spacious feeling with floor space under the vanity for scales, waste paper basket and slippers (and/or open under bench for a tall clothes basket?) and enough storage space inside for towels, toilet paper and cleaning products and a super generous 1800 wide mirror doored in wall cabinet for toiletries and no need for a privacy screen for the toilet and add a fixed pane of glass pane in the new wall above the cavity sliding bathroom door up to ceiling height ...like a "window" between wiw and ens to help spread the light from the skylight when the bathroom door needs to be closed and the old bathroom door opening could be used to add a cavity sliding door (ie inside the wall not sliding outside the wall) between wiw and bedroom if you need one ..shoudl be a much better ens and wiw and hope to see the results