Hi veto,
I will answer your second question first, I used only 1 ID to do all the work, except I sign up with Blum Kitchen myself so I just get the kitchen ready for Blum Installation and I called them to come, just took 1 day to install. I also signed up with Evorich to do my platform bed which I also get the room ready for installation and arranged them to come.
Your first question is tough to answer, its hard to break down to how much each room cost. I planned my budget by having a list of items i need for the house In excel and I keep maintaining it as soon as i got a quote or made a purchase. I can clearly see how much total I am spending on the house. I will attach here for your reference, You can try create your list too so you can visualize.
As you can see I spend over 50K including minor household items which I didn't put into the list. I will elaborate on the Total ID cost of 20,830.76 which I paid to the ID. This sum consist of :
Painting 1200
False Ceiling 500
Living room Cabinet 2000
Besglas 1.6m Wardrobe 2000
Granite worktop for kitchen 1400
Overlay WC flooring 950
Masonary work in toilet 1200
Granite Worktop for WC 750
Sliding Shower Screen in WC 800
2 new Besglas toilet door 1160
I can estimate I spend about 6000 on the toilet and 7500 on kitchen.
Hope I answer your question this way can give you a better idea to work out your budget. I only have one advice to you which is if possible, reduce the amount of carpentry work to minimum as they are expensive and hard to replace them few years down the road when they deteriorate. You will see a huge chunk off your ID cost if you don't do carpentry.