Hi Im Japanese (studying in the Uk) and maybe I can help out alittle.
The truth is that many Japanese actually KNOW some basic english BUT are too shy to speak it. So they actually do understand you if you speak slowly but they may just try and avoid you!
If you go to Akihabara, depending on what you are looking for, you will need to go to different stores. The best ALLROUND store is the MULTIMEDIA YODOBASHI CAMERA which is like a megamall only selling electronics. However the only way to make it worth while to buy it here is either
1) Get the gold point card (10% point back system, i.e. you buy PS3 40,000Yen, you get 4000 yen to spend in store on anything). Sometimes they have promotions of 15% etc. Drawback is that you need a Japanese address...
2) Tax refund can be done so take your passport! (But you cant get tax refund AND points).
If you are looking for computer parts go to ARK computer and TWOTOP, they sell loads of computer parts at very good prices like Motherboards, Graphics etc. (In akihabara)
If you like Japanese collectable figures, go to asobit city also in Akihabara and RadioKan for really rare ones.
If you want to know where 'fashionable' people buy their clothes, it is in DAIKANYAMA which is 1 stop before Shibuya or URA-HARAJYUKU which has famous labels such as Porter, United Arrows etc.
Omotesando is also amazing for shopping though very high-end. (E.g. Prada, Gucci etc)
If you want cool places, go to ODAIBA preferably with a girl and preferrably at night hehe. Take her to the Bar-Bacoa restaurant, have a nice meal and take her to the cinema. Very beautiful scenery etc.
Hope that helps!