Don't worry about finding the right trains/platforms. All of the major and most minor stations are very well signed in English. Plus, you can just show your ticket to the entrance gate attendant and they can tell you where to go.

If you know in advance what trains you want, you can make seat reservations for your entire trip, or any smaller segment, at the Japan Rail Service Center at any station. If I know what I am going to need, I like to drop in there upon ARRIVAL at a new location, before heading to my hotel, to obtain tickets and seats for my next rail segments - even days in advance. That way I have them and don't need to worry about sell-outs or last minute bad seat options. Many others here prefer to just wing it and get tickets just before boarding. YMMV.

I recommend having your preferred trains written or printed out ahead so you can just show the JR agent when you reserve your seats. They often can understand your needs seeing it written out in English better than trying to understand your spoken English. Hyperdia is great for this.

I have never used a concierge for train tickets or anything else so can't make a recommendation there.