The choice of the bellows shade is a tripod choice, can be hand held but ungainly. It does, the latest anyway, drop down whilst staying attached to change lens fitting filters/polariser and fits drop in filters. Especially useful for neutral grads where you can adjust the "horizon" position.
You can stack 'blad filters. They bayonet onto the internal bayonet on the lens and the shade bayonets over that onto the external lens bayonet. (what a lot of bayonets).
The polariser must be last, it does not carry a bayonet to allow a stack over it.
Whilst you can mount other adapters etc I have always preferred to stay with original gear. The cost difference is usually minimal S/H and there is "something" (despite the Lunar) of having HASSELBLAD plastered over everything.
You can of course go a bit too far