Overall, I would say it's a pretty successful first attempt at mead making. Congratulations!
1) Process is good. There's lots of flexibility in any process and what I do, someone else doesn't. I like the idea of no-heat mead making - keep all that goodness in the brew - but at 120 you're touching on as hot as you'd want to get. Make no mistake, I've made fantastic meads that were fully pasteurized at 160, just lacking some volatile aromatics that went away during the process.
1) I think you're reading timings are fine. Mead can be slow - I prefer it that way. Mead is what just sits while all the beer is being made and drank. It make the end result a little more rewarding
1) Your nutrient additions could have been a little more frequent. IIRC, my additions all take place within the first 4 days or so. IIRC, about 50% after lag phase (8-24 hours), about 35% at 1/3 sugar depletion (about 24-48 hours), and about 15% at 1/2 sugar depletion (about 48-96 hours). After 1/2 sugar depletion, my understanding is that the yeast is no longer able to use/assimilate the nutrients therefore they provide no help in finishing up the fermentation.
1) Your initial ratios strike me as a sweet mead, which is fine. I like sweet meads and my wife loves them. I don't quite follow your fermenter volumes: 3.5 gallons H2O plus 1 gallon honey = 4.5 gallons of mead. But you only indicate you got 3.5 gallons total split between two fermenters.
2) It seems to be an alcoholic, sweet mead. Were your gravities taken with hydrometer or refractometer? I see nothing wrong with your proportions or the end result. Yes, it will mellow out over time. I have many year old meads (5+) and they are fantastic. I'd say in one year you will find this beverage to be significantly different than you find it today. Good work!!
3) No, don't dilute. If you want a lighter-weight mead, make a new one with less honey. Don't spoil a good thing
4) Fruit additions are usually best added in a secondary after racking off of the gross lees (i.e. after racking off the sediment). You'll maintain more of the real fruit taste and aromatics that way, but get less fermentables (which is fine in your case). Fruit that's added to the primary loses a lot of it's character during fermentation, on the other hand it adds to the fermentables. Quantities I'm uncertain about - do some searching, I'm sure you'll find some good rules of thumb. If it were me, I would keep your large quantity unfruited and only fruit your small 1 gallon (that's just me).
Again, everyone does things differently and you did just fine.