I see a recipe for disaster.
Sourcing your own wood and equipment etc,
Getting a 3rd party to cut wood
Getting someone else to install everything
WW3 will start when the sink doesn't fit in the hole, when the cooker doesnt line up with the gas supply, ......................................
Of course - it is never the fault of the person who ordered the materails !
Its best not to micro-manage (thats when you upset the workman and he walks off leaving a party done job), tell him what colours, designs etc that you want, let him source the materials (he'll get a trade discount so he'll make a bit more money, even if he charges you the retail prices) let him cut to fit and let him install.
Only one person to blame when it doesn't work.