With regards a black suit I'd say a charcoal grey or a navy suit are far better options. Black can look quite stark and formal for anything other than a funeral or a fashion shoot. It's also not that flattering on pale skin. Another point to make is that you'll find it very hard to match a new pair of black trousers with your old black jacket. There are many shades of black and the two are likely to look different from a medium distance.
There is no actual definition of tailored and regular. Most shops use the term differently but in general a tailored suit will be slimmer in the waist. A regular suit should be more roomy in the waist. Some places also refer to slim suits. These will be slimmer everywhere including arms, legs, waist, shoulders. But as there is no actual standard for slim, tailored, regular, etc, then every shop is different.
Either way, if you do get a whole new suit, I'd recommend getting it adjusted. Even a cheap suit can look good if adjusted and an expensive suit can look awful if it doesn't fit right.
