So with my job (pm in construction) and do budgets etc this is roughly what I would work to (apologises it’s long! )
Install 18 double socket plugs - £150 ea £2700
Reinstate 2 double plugs which currently have blanking plates - allow worst case wiring has been removed £300
Install spot lighting in 9 rooms. Roughly 50 in total. I’d allow
£300 per room plus cost of fittings say £50 to allow their mark up - £450 plus rooms £2700
Remove 11 pendant lights - I’d allow maybe £50 per fitting £550
Replace 1 ceiling fan with new one. I’d allow 1hr labour plus cost of fan plus mark up £40 plus say £100 for fitting
Install 3 outside plugs - depends how long a run you have from point to house I’d budget as a min £200 per socket £600
Update junction box £100
Install 2 outside lights - if nothing there already I’d allow £200 per fitting - £400
Reskim 4 bedrooms, 1 living room, 2 office spaces and hallway including ceilings - no idea but checked on check trade avg cost they suggest £24 per Sqm - and advise £1100 for a small room and £1900 for a large room - so averaging your rooms at £1500 - £7500
Redecorate reskimmed rooms. White paint and white gloss for woodwork excluding doors. I work on a rate of about £10per Sqm for walls
/ceilings and again for woodwork - but obvs don’t your Sqm for rooms. Again check on checkatrade on their price guide - they allow £1600 for a hall, and 450 for a medium sized room - so say £3600
Replace 13 radiators - allow £200 per radiator and then cost for radiator and mark up - £2600 labour then just plucking a random value for a radiator say £150 each £1950
Replace hot water heater- say £150 labour plus heater
Replace skirting board and coving as recommend by builder for reskimmed rooms. - we allow £50per lm - so say £300 each per room to average it £4800
Install 3 air con units. £9k - this is based on daiken units which we have to use at work so probs can get a cheaper brand. But I installed 2 wall mounted units and external wall mounted to an existing system and we allow £5k per unit when budgeting but have longer runs etc than you would in a house
anyway hope that helps but definitely get some quotes as I would be looking around £40k