An accountant friend of mine who used to have his own accountancy firm always gave out 3 pieces of advice to his clients
Never trust a solicitor
Never trust a bank manager
Always trade as Ltd
Now, as much as I agreed with him, I do have a slight caveat on the 3rd piece of advice. Some micro businesses can be perfectly ok running as a Sole Trader.
The main things to consider on whether to be Ltd or a ST imo is (and they are both based on the size / profitability of the business) :-
Pros :
Liabilities - With a Ltd company the company is the legal entity and thus liable for any debts. With a ST then you are the company and you are personally liable. So if you are working with extended credit lines from suppliers and customers, then the greater the amounts you are working with the greater the personal risk for a ST if the business fails.
Profit & Tax - It is much more tax efficient to be a Ltd company than a ST. With a ST, you get your personal allowance then you pay Tax & NI on everything above that and will go into the 40% band if you are profitable enough. With a Ltd company, you become the director and can pay yourself a minimum wage to just tick over your NI contribution for the state pension eligibility and then take any other money out as drawings which can be allocated out of the profits a dividends. The company just pays Corporation Tax on it's profits. They have tightened up the rules on this, but it is still more tax efficient over a ST, especially when profits start rising.
Cons :
There is more paperwork and bureaucracy involved in setting up and running a Ltd company than just setting up a ST, you will be best advised to employ the services of an accountant and the overall fees for submitting a Ltd companies accounts will be higher than for a ST.
As for doing it on your own and/or employing someone at a later date, there is no difference between a Ltd or ST - you can be the sole director of a Ltd company (though you will need a payroll scheme to run for just yourself - as you are an "employee" of the business) or work alone as a ST and you won't need a payroll scheme until you employ someone else.
You can always start as a ST, see how things go and convert to a Ltd company at a later date if you wish.