Using triple National deeps is routine with me and essential flexibility of expansion and contraction won't be given by one heavy 14x12 box, unless you're lucky and the box matches the laying rate of the queen at full speed. If you use good Buckfast queens a 14x12 is unlikely to be enough.
Although, if you, like me, run your 14 x 12 hives without a queen excluder (it works ..) then you will have enough space for the most fecund of queens. When they shrink back into the brood box in readiness for winter you have more than enough space for stores to see them through and you eliminate having to inspect two brood boxes or more through the season. There's always more than one right way to keep bees - but it's a confusing start for any new beekeeper.
As JBM said, do a full course in spring; any practical knowledge you gain now will be forgotten by then. A taster day this year would be valuable if you haven't been inside a hive before.
Totally - so called 'intensive' one or two day beekeeping courses are just great money earners for the people running them but they really are just tasters - there's a lot to take in and cramming it into a day or two ... not good.
True, but that will contribute to valuable experience. There are three points in the year where beginners fail: swarming, varroa control, and over-wintering.
Couple of years ago a customer turned up to collect a nuc and I discovered that she'd not done a training course, read a book or been inside a beehive.
She was positive and young enough not be fazed by her lack of knowledge and the bees came out of winter having been upgraded, fed and treated on the back of a few WhatsApps and reading Haynes. Mind you, she did a full course that spring.
They were one of the lucky ones ... I've seen more with dead bees in the spring and the devastation and self recrimination it brings to a new beekeeper. You would be far better advised to start in spring and watch a new colony build as the year progresses and ready them for winter having a few months of beekeeping under your belt and having completed a proper course over winter.