Congrats on the bike. There's basically no penalty to using mtb shoes/pedals on the road. Any soft soled shoes (mtb or road) will be prone to hot spot issues and poor transfer.
I have really wide feet (EEE) and wear Sidi Genius Mega road shoes. For mtb I wear Shimano XC5 lace up shoes. There was a short break in period, during which I used my handy dandy shoe stretchers (if you have wide feet and don't have a pair, get a pair) and for the last 2 years or whatever they've been perfect. They're inexpensive, quality, durable, they look sort of road shoe-ish, and the laces give a lot of adjustability. They're very walkable, and though no world tour pro would use anything other than the stiffest sole available, these are plenty stiff enough for aggressive recreational/amateur race riding. Widely available for under $100 online.