Diets are a very personal thing and obviously you need to figure out what works best for your hamster. I personally feed 3 different brands mixed together for my hammies (I have a Campbells plus I breed chinese). I use JR Farm Feast for Dwarf Hamsters, Best Pets and Vitakraft Hamster mix
In terms of toys you can't go wrong with some good old bendy bridges! Those and cardboard tubes a re a firm favourite with my guys and egg boxes too. Terracotta plant pots make nice hides and are good for wearing down little claws plus any toys with multiple exits work well too