I moved from Russia 4-5 months ago and my billing address is still based on the Russia currency/store. I know that buying games on another store while your ip is on another country puts it on region block, but is it the same for buyable items in game?
This varies on the game. Some games have a fixed currency and price (in that case, you just pay the equivalent in your local currency), while others opt for regional prices, just like games on the store.
For example Phantasy Star Online 2 AC/SG packs have regional pricing for microtransactions while Path of Exile is fixed to the US Dollar.
As far as restrictions go, this depends on the game itself. As far as I know, no game has restricted the things you get from a microtransaction based on region.