The lenses come in 2 filter sizes but in a few different models where coatings improved. The early series were chrome and black plastic M series had a filter size of 58mm. The newer lenses black plastic are 62mm in the P series. Hoods came in snap on rectangular plastic shaped as well as rubber colapsable.
Backs come in several updates. Not much has changed in how they work but surface appearance has changed slightly with single locks vs double latches n side winders. Otherwise they are all about the same. Oh and I believe there is a morized back as well you may want to look into, I've never had or used one.
Cranks are all about the same and are harder to find or expensive. Many people miss place them so they are lok socks in the dryer.. lost forever in a black hole with lots of battery covers, another lost item of who know where it went.
View finders haven't changed much but prisms have to a slight degree. They have meters n an automatic mode that will adjust exposures for you. The difference is the electronics in the meters as the glass is the same. I'd rather uise a hand held over metered prisms.
Take a look at KEH online catalog to find all the varieties of accessories and you will be amazed how much is avalable at bargain prices.