Greboruri
Kiznaiver
I think if you can already buy it online at a cheaper price including shipping, don't bother buying it over there. As for getting stuff home, I usually try to pack it all in my suitcase and not try to go over the maximum weight. On my first few trips I just sent the majority my stuff back via EMS through Japan Post to my mum marked as a gift to avoid Australian Customs taxing me. Admittedly this is quite expensive but does have the advantage of insurance and tracking. Other options include Airmail, Surface mail and Economy Air. Some have the option of insurance and tracking, most don't.
Tip in regards to your suitcase; send it back to the airport via Takkyubin. Your hotel can do this for you or you can just rock up to any of the Yamato Transport offices (aka Kuroneko) and do it there if your staying at an Airbnb place. Depending on where you're staying, you may have to put your suitcase in one or two days early so it reaches the airport on the day of your departure. However it beats lugging your suitcase around on crowded trains on the final day of your stay, especially if you have a late night flight.
With Akihabara, it really has changed over the years I think. It's really crowded now, even on weekdays which wasn't the case when I first went there six years ago. Don't go on weekends. Just don't. I would also do some research in regards to shops you want to hit, as wandering about is a bit pointless and the place can be exhausting. It's a bit hard online as there is no definitive guide to shops in the area and shops can open and close at a fairly rapid rate. I was going to suggest going to the Tokyo Anime Centre to get a map of the area, but bafflingly seems to have moved to Ichigaya (?!). Finding a restaurant at lunch can be damn near impossible. Totally avoid the lunch time crowds, have lunch early, way before midday. Can't stress this enough.
Anyway, some of favourites in the area; Shosen Book Tower for artbooks, Yodobashi Camera for discounted new DVD, BD, games, figures and model kits, Lashinbang for used DVD, CD, BD, figures and merchandise, Trader for really cheap secondhand DVDs, BDs and games, Lammtarra and Mulan for cheap new BDs, CDs and figures (small range, on ground floor, porn and other stuff on floors above...), Mandarake for everything, X for used figures, Book-Off for used CDs, BDs, games, manga and artbooks, and Suruga-ya for used DVD, BD, merchandise and figures, used games, and used anime, idol, doujinshi merchandise. There's a lot more of course but that's all I can think of for the moment.
I'm heading back to Japan for Wonder Festival Summer 2018 and Comic Market 94 in late July/early August and to see all the festivals around Tokyo in between those two events. Got flights and a really nice Airbnb apartment in Kanda, Chiyoda all booked.