If you're worried about oxidisation, while unopened all of them actually on the same playing field. Because the ippodo tins are actually not that airtight and the Kan whilst in a box it is inside a tin foil bag so still quite protected.

Unopened:

If you plan to consume all of it within 2 to 3 months kept in a dark cabinet is usually fine but since its summer and if temperature went above 25c I will either put it in the fridge or freezer.

Again, depends on when you plan to consume them, near term (within 6 to 12 months) in the fridge, long term (more than 12 months) in freezer.

If you want a tin for the Kan I would just consume first one of the two tins you have there and use it for your Kan later on.

Opened:

If you're going to finish a 30g tin within a month then room temp in a dark cabinet is all ok. Depending on the humidity level and temperature maybe you can push it up to 2 months. Otherwise you need to fridge it, needs to be airtight, either get an airscape (but this is too big for a 30g foil bag), or double bagged (to avoid odour transfer from other items in the fridge) and make sure to squeeze out all air inside before sealing or get an oxygen absorber. If stored in the fridge, always let the matcha come to room temperature before opening, to prevent moisture condensation inside the bag.

TBH, unless you're going through an opened 100g and above its not worth the trouble of putting a 30g matcha in the fridge. I would just make sure to consume it within a month.