welcome welcome here ^u^
yes correct, since the applications are spread out over 30 minutes, there shouldn't be server issues. I recommend to use Firefox, no other tabs open and use a PC, not on mobile. Also, keep on a .txt file some of your details (email, address, passport, card payment number, etc..) so it's easier to fill the various forms. Have also a "plan B" if your hotel or day is sold out, think in advance of another hotel and day.
As I wrote earlier, usually the most chosen one is Tokyo last day evening, so if you plan to attend that, yes try that first. The day concerts are a little easier (because more people choose first the evening concerts), and you can actually enjoy the concert more with the day show, since there are more students, families and couples attending that.
And yes, that's a very good idea to try Osaka first! Then, if you don't know where to stay for cheap between your days of Osaka-Tokyo,then you could think of choosing for example a guest house or apartment stay at Sakura House, it's much cheaper compared to hotel stay, I've used Sakura House Tokyo many many times, always excellent!
SAKURA HOUSE® - Furnished Guest houses, Apartments, Share houses for rent in Tokyo, Izu and Kyoto since 1992.
(apartment you have your own room, while guest house usually you have room+shared kitchen and shared bathroom. Then you have the laundry, usually coin laundry in a shared space, and the fact you can have a kitchen save a lot in terms of money, and is so nice to actually go to japanese supermarket to buy foods to cook. Each room has wifi and all bills electricity-water already paid, you also have your own address, so you can order both food delivery and package delivery, for example from Amazon JP, it's so nice experience. On the website you can see the monthly prices, but you can stay 2-3 weeks)