there is no perfect dimensions for an island. Try to organce space subdividing into smaller cabinets of 60x60 cms which is the max space for a structural division and works for seating area as well

Based on the dimensions you have given and the religious aspects you mention you are very restricted in what the layout can be. The best solution I see means you have to move the door towards the south by 36". I suggest you make it a pocket door retracting towards the south wall. This leaves 36" x 60" of space on the north wall for either a shower or tub. The vanity would be on the west wall ( across from the door) spaced away from the tub or shower around 12". Make sure the vanity cabinet is shallow, no more than 21" deep. The vanity should be able to be about 48" wide. The toilet will go on the South wall with the right side of it close to the East wall. Code calls for approx. 33" of width for the toilet overall. If budget allows you could continue the vanity cabinets into the corner of the south wall however keep in mind that most of that area that will be next to the toilet and not easily accessible. But it would provide extra storage or counter space. The sink will have to be centered in the 48" part of the vanity. You could also frame out the southwest corner to capture the side of the vanity instead of a longer vanity. Hope this helps.

Thanks a lot for your comment. I wouldn't exactly call it a walk in-closet. As you can see from the drawing, Its space provided for two single wardrobe (one on each side). Maximum width can be around 3.5 ft. The humidity point is quite relevant. The question is would it be possible to include a wet room in the space i.e. 6ft x 8.6ft. - considering I don't remove the dress wall. Wanted to get a sense on the possible layout. Thanks and look forward to your advise.

I suggest you follow the step-by-step guide for creating storage cabinets under the bathroom sink. Take proper measurements - Measure the available available space in height, width and height. Cut Plywood to size - With a circular saw and framing square, cut all the required pieces out. You can use a sliding compound saw as an alternative. Attach the base and sides - Start assembling the sink cabinets by placing the bottom piece of plywood sheet on a flat surface. Attach the back and top boards - Place the plywood sheet for the top part of the cabinet and attach wood screws to connect it to both the sides. Turn the back faces of the cabinet upwards. Keep the back piece over the structure and fix it into place with wood screws. Attach shelves - Place the cabinet in an upright position to install the shelves. Slide a shelf into the structure so it is flush against the back. Attach door - Keep both hinges of the door on the same side of the plywood sheet. Drill them using wood screws into place. Now keep the door over the cabinet structure, extend the hinges to one of the side panels and fix them to make them secure. Fix a hasp closure on the other side of the door, placing it in the center of the hinges.