I could probably give you some fairly accurate costs in a week or two if you send me copies of the quotes you get........
Also I'm going to start trial them on a small job to start with - do you agree that's good practice unless they've got a really good sterling reputation
You could ask the electrician to wire a plug, the plumber could fix a dripping tap, kitchen fitter could quickly fix up a wall cupboard for you?
You are seriously overthinking all this and focusing too much on the process.
Are you in a position to tell these trades people what you want: Electrician - how many sockets, light fittings, switches and where, especially in the kitchen - circuits for oven, hob (gas/electric) spurs for appliances, extraction etc, cheap fittings, branded white, posh stainless steel?
Plumber - plastic or copper, cheap, branded or designer fittings, location of sink, washing machine in kitchen, shower in bathroom electric or off boiler?
Kitchen - supply and fit or labour only, dirt cheap off the shelf flat pack or slightly better
Wickes/Howdens etc drawers vs cupboards (one a lot more expensive than the other), quality worktops, tiles from the clearance pile, appliances built-in, freestanding, budget or branded?
Plastering - cheap overboard and skim or proper wet job?
If you don't have this information you're going to struggle, you won't know what you're getting and which represents best value. You need to pin them down on timings and availablity - when you need their price by, when can they start, when you will let them know they've got the job.
If you have 15 various trades people round your house in a week it's probably going to make your head hurt, you won't remember who said what and when!
As there doesn't seem to be much of a time element for this project I would just start with the electrician - you'll need to decide on the oven/hob in the kitchen but he can just run a few basic circuits in for the rest and pick it up later, for the rest a decent tradesman should be able to advise on what is standard and what is nice to have, eg I have £250 worth of LED reading lights above my bed because it's my house and that's what I wanted.
You'll get the best prices if you present nice tidy self-contained "jobs" - electricians will love an empty house with floors up/ceilings down and positions of all fittings drawn on the walls, plasterers like empty rooms, switches and sockets removed with cables tucked in back boxes, most of the power in the house off etc.
Decide whether you want to be in charge of waste - bathroom fitter may charge you £250- 300 for a skip (he'll pay £200) and it'll go off half empty when you could have just dropped the old suite off at the tip yourself, next trade in will repeat with another skip at your expense!
You also seem to have an idea of giving budgets to tradesmen, eg telling a plasterer you'll give him £400 to plaster a room, I'm not sure how well this will go down but I'd be interested to find out.
Good luck. If you ever get started you will learn a lot more by getting your hands dirty than you can by speculating on this forum.
