I always followed the guidance of finger food being roughly the size of an adult finger.
Maybe try some roasted veggies which will be 'hard' on the outside if he seems to like the dry/hard foods. I made potato wedges, sweet potato, carrot, parsnip, turnip, butternut squash...basically anything that can be roasted, the outside will be dry and crispy whilst the inside will be soft like a mush/puree.
You could also try 'drier' foods such as small pancakes, mini muffins (made with sweet potato or carrots for example), meatballs, bean cakes/fritters, oaty chews.
I agree with pp that the smooshing of food is all part of the learning process, offer few pieces if you are concerned with waste. What helped me too was to realise that every meal time was an 'activity' and a learning time, all those tastes, smells, textures, plus exploring the physical nature of the world around them. To a LO it is all new experience and not 'just' a meal.
How much do I interfere with his playing of his food?
I only stopped mine from dropping or throwing to the floor. I'd quickly hold his hand before the drop or get a plate or bowl underneath it fast and say "tidy up please" then when the piece dropped into the bowl "oh thank you for tidying" and repeated this at the end of each meal where he would help me collect the discarded food around his tray and pop it all back into a bowl or plate before we washed hands and face. Making it part of the routine.
