Can I run more than one kitchen display system, one for the grill and one for the drinks bar?

Yes, as many as you like, because the yearly price covers every device. Pair each screen under Settings → The POS as A screen in the kitchen, then on each screen tap the station button across the top so the grill screen shows grill dishes and the bar screen shows drinks. Set up the stations first under Settings → Printing & receipts and set Who cooks it on each dish. A screen left on Everything shows every ticket. The Tables, tabs and the kitchen screen tab in the docs has a guide called Set up stations.