In all honesty, if you want to flip 3-4 a year, you need to be able to buy 3 or 4 and renovate in one hit, from a spare cash point of view
it takes a few months to buy realistically 3-6 months minimum for a full refurb and selling a house is just a joke, 3 months completion time after usually 6 months for sale if u start at a top end price, that's a year each
my best advice if you have cash to buy outright is just don't bother, finance is king, split it into deposits and refurb cash, interest rates are less than 3% if you shop right and u can make 10-20% minimum on property flipping easily if your smart, makes sense to borrow 500k and make 20% on that figure rather than the 100k cash u may have hanging around
the BTL game is a long one, most people use it for retirement, as your not going to get rich making 200 quid a month on the rent per house, although if you buy 10 and pay them off over 25 years you would be a multi millionaire by retirement, so that's a thought
for the record I have 17 properties at the moment, most rentals and I flip a few a year, but my best advice for flipping is to buy the biggest house you can afford in the best area, the ceiling price for the property with be vastly higher than the small terrace properties and profits are crazy in comparison, making 100k per property is regular on larger properties but a small terrace is never going to make you more than 30 odd thousand really more like 15-20k in real life
also homes under the hammer is legit, I have been on it myself in 2013 and made 36k on a semi in 7 months,
happy flipping