i read in a pig husbandry book " the first profit is the best profit" ie sell them as weaners if you can, as the profit / labour is better than fattening them etc.
you do need to have enough money available to finish/kill/butcher the weaners before you receive any money in sales.
I'd echo what others have said. The weaner market is relatively small compared to how many weaners you might produce in a year - most smallholders want weaners in spring. But to make money, you have to have your sow producing as often as possible (you're feeding her anyway) so you will inevitably have autumn / winter litters.
You can't rely on selling all piglets as weaners - if you can, at a reasonable price, fine - but you have to have a Plan B which involves taking them through to killing and selling the pork / bacon / sausages. Otherwise, you end up selling them for a fiver at the market. Someone might make money, but it won't be you.
Adding value - ie processing - makes more money BUT if you have to pay a butcher to make your bacon and sausages, that eats into the profit big time.
Not very positive, I'm afraid :-(