That looks a lot like the layout I used for the 5E3 head I built a year ago.
I don't see a square hole where the AC goes in on the back panel, instead I see a round hole where it looks like you'll put in a strain relief bushing for the power cord. One thing to consider: use an IEC plug for the mains instead. I never regretted doing that on mine.
I changed out most of the carbon comp resistors in my 5E3 head with metal film resistors (initially was 100% CC.) The only change I noticed was less hiss. I left in all the 220k and 100k CC resistors, where they supposedly matter (mainly the plate resistors). The amp *really* hissed with all CCs. Even if you replaced only the cathode resistors with metal film, I'd bet you'd notice less hiss.
Can't speak for the 120v pilot light, so long as it works who cares?
Just to compare notes, one year later I am modding my 5E3. Why? I don't need the touted interactive volume controls; I just leave the unused volume at about 2 O'clock. I also don't need the second channel. Never use it. I am going to use that extra triode to provide a different pre-amp voicing which I can switch on and off. I am also going to replace the unused channel's pot with a resistor.
I'd recommend building as stock as you can, then tweak as needed. I ended up undoing a lot of mods I built into the original build. But definitely replace the first two coupling caps with something like .02 mfd instead of the .1. With the .1 caps, it's just too dark and muddy with humbuckers. If you play yours with buckers and it's too dark, that's the fix.