Well, there was someone else asking about the shipping thing, and my advice was just get whatever you need from here man, you can find all the brands you need in here, and with MUCH LESS prices if you're gonna put the exchange rates in your mind!!
As for the shops you're asking about??? you're Egyptian!!! you should know that shops in here sell almost EVERYTHING! even if they didn't have it??? all you gotta do is just to ask the shop's owner if they have it! if they don't??? trust me, they will get it since a customer asked!! they wanna sell man!!!!
And for the PO Box thing??? the local post services people in here know almost all the addresses in the area where they're assigned, and it should be less hard for you, you already speak Arabic!!
I understand that you left Egypt long time ago, and I know that MANY things changed here, specially people's minds and integrity, but trust me, it's still the same when it comes to bribes, sorry, TIPS, that will make ANYTHING happen in here man, so just be generous with the Post office people and they will get your address right every time you got something sent to you.
As for the customs, they tend to exaggerate, dunno if they got rules for things like cloths and stuff like that, but if they don't??? that means it would be up to the customer agent in charge when your shipment arrives, and of course you won't be there to give him/her tips, so probably your customs' bill will be high!
Just go walk around the streets and get to know more people or just watch them getting their stuff done, I'm sure that would help you more than being online talking about it, not many Egyptians in here man, so you won't get the kinda help you're looking for.
But I wanna give you a free advice about something that you did not ask for, DRIVING in here, cause I had friends working in Gulf area, you just need to know that you're gonna need to forget all manners when you're driving in here, if you wanna reach where you're going on time??? you just need to loose all driving manners, or else you'll be stuck!! and I'm NOT talking about manners towards drivers, but manners towards traffic laws, specially giving a signal when changing your lane or taking a turn, your hand going out of your window will be more helpful!!
Hope I could help, good luck surviving in here dude!