Deefadog,
I am nearing completion of a very similar project, so may be able to advise.
IMO your estimates are generally too low. I started by removing wall paper, which ended up leading to the removing of plaster and render on every wall right down to brickwork. Then I thought that if I was going that far, I may as well remove the old ceiling boards. In my case I then removed some internal walls and built new stud walls. If you have the plaster off and ceilings down you may as well replace the electrics and possibly some plumbing and old radiators. A new bathroom meant replacing the old floor boards with WBP for tiling onto .. why not some underfloor heating..
You see where I'm going? when you think it's a small job, it gets carried away and won't be as small as you think. Using this forum, I did almost all of the work myself, which saved a hell of a lot of money - but bare in mind it's time consuming and tiring. I did all demolition like removing old plaster and ceiling boards. Put up new ceiling boards, preped walls, ran the electric cables etc etc. I used the professionals to put on the new plaster and connect the electrics. Fortunately in my case the electrician was a friend, so was free.
There will also be some surprises. I took down the old ceiligns to find my rafters were rotten, so had to put in supports.
My ball park estimates on what you asked about are:
kitchen - about right for entry level.
plaster walls and ceilings was £5 m2 for render and £6 m2 for plaster - that is as cheap as it gets I think and I used a Polish contact. That excluded materials which topped out at a good £500 plus a bit.
New combi boiler fitted I got for a little over 2k, which again was on the cheaper end of the scale.
We put in a good quality bathroom suite. I bought the suite for £800 on sale (it is decent not entry level) and has units. The taps are what get you and we had a 3 way diverter and overhead shower and the taps alone cost another £800, but believe me, you notice the difference. Any plumber will say - spend money on your brass (taps).
Then there is the cost of materials and some tools, but those are surprisingly cheap. They do add up though!.
One word of advice if at all possible try and wangle a trade card for Travis Perkins or B&Q or who ever you choose. It saves a lot on bathroom suites and kitchens etc.
Like I said, it can be done cheaply if you do it yourself and you feel much better about the end product, but it is a lot of work. Taken me best part of 6 months, every weekend and most evenings. Don't be put off though, it rewarding if you're up for it and have a slight hands on approach to life. I haven't plastered downstairs lounges yet either. That is largely just the upstairs of a 3 bed semi. I reckon I've done it all for probably a fifth of what a bulder would have charged for the same job.