If you are developing, as opposed to doing up and re-selling what for the duration would be your private residence, then there is no chance of it falling under CGT regime, so it would be income tax which applies, or it would if you were a sole trader or partnership. As you're to operate as a Ltd Co, the company would pay corporation tax on profits after expenses, and then its owners (you) would pay tax on dividends the company pays you.
None if the tradesmen are contractors. But if you take them on as employees, you have to pay employer's NI contributions at 12.8% of earnings in excess of £89pw, plus of course you have to administer employee's NI and income tax.
Of course. Profit equals income minus expenses. You pay tax only on profit.
Suppose you buy a house for £50k, spend £10k on materials and services, and employ your dad for £20k and yourself for £5k. You sell the house for £100k. Then the company would have made £15k profit. You and your dad would pay income tax and NI on your own wages, and the company would pay nothing for the first £10k of profit and 23.75% Corporation Tax on the other £5k. You could either leave the remaining £13812 in the company as working capital to help buy the next ruin, or pay it to yourself as dividends, on which no further income tax would be due by you unless this would push you into the higher tax bracket (and if it did you would pay
25% of the bit that's over the threshold).