No, not a problem. Just show you're willing to buy and they'll be more than happy to sign you up.

I did find Yodobashi, Bic, et al, to have lower than MSRP prices. I was able to get both duty-free and points for a large purchase at Sakuraya.

While Akihabara is the most well known, going to the same stores in Shibuya may be easier while netting the same prices.

I haven't been to the Costco but, to me, Costco is Costco. If you want the latest stuff, you don't go to Costco.

You're right about voltage. If it uses a brick, it's fine. If the voltage converter is built in , there may be some performance issues. My rice cooker lasted 7-8 years in Cda before it died on me.