Can you say a bit more about what you would like in your bathroom - shower & bath / over bath / shower only / bath only? What type of sink are you thinking about - pedestal , wall hung, floor standing vanity? Thinking about what you would like will help with layout. Also a small plan of your room with window & door positions would be great.

This room should provide plenty of space for everything you are looking to include, without it ending up being too crowded. There is enough space to both sides of the window for a shower, but the window also provides an ideal location for the free-standing bath. The small bite taken out of the room by the adjacent cloakroom provides the potential for some interest, perhaps with counter-height bulkhead to conceal a cistern and have a semi-recessed wash hand basin. Good luck.

As Jonathan says, you start with the Soil pipe, and if you've agreed with your bathroom fitter that he's able to put the pipe across the wall behind the toilet and under the bath to get to the outside wall, then that's fine, but if not, you really need to discuss it with a professional. There are many reasons and regulations that you need to stick to with regards placement of soil pipes, because sometimes you need access to unblock them. When designing a bathroom, it is important to know where you have to have some items and then decide where you can put the other items that you want. Check the soil pipe situation as this dictates where everything else can go. I suspect unfortunately, that if you can't solve the soil pipe problem and the toilet needs to go on the outside wall ( which is the normal place for it ), then you may have to have a re-think and possibly change what you have purchased. I've tried to have a re-jig with what you've purchased and moving the toilet to it's normal position, but i can only make them fit if you do what Jonathan suggests. Even then, I would suggest that the door be moved along the wall to accommodate the tall unit. You will have pipework from the vanity that you need to box in, it can go under the bath, but at least it's just water not the soil pipe. I would have also considered a bath to fill the whole gap of 2000mm not a 1700mm, but you can use the gap to build a space at the end both covering the pipes and giving you somewhere to stand toiletries. The taps for the bath aren't marked, so i'd probably put them on the bottom end nearest the vanity on the flipped plan below.

If you don’t need the extra bedrooms yet then leave it as it is. If you split the front room into 2, then your new master bedroom in the middle becomes really small and won’t have the wow factor.. You’ll probably only be able to get a bed and wardrobe in there. You might as well enjoy the space while you can. If in the future you decide to extend into the loft and use that loft as master you can spilt the front bedroom then or put 2 rooms into the loft.