My bike is a Rize RX Pro, which started out life as an Ultra powered fatty. It's since had the fat front pogo stick setup replaced with a cheapy (125. or so from Amazon) 100mm wide hydraulic front end (for my nearly 100% paved/packed riding surfaces), then new 27.5 hubs and wheels were built to use with 27.5x2.8 Schwalbe Super Moto-X tires.
Ooh, that layout sounds fun as heck!
And going hydraulic is surely a good move? I suspect I'm a bit large for most air shocks to provide the damping I'd prefer.
I didn't have too much concern regarding chain ring sizes. There's room on my bike for about anything I would ever want to run - but I hadn't considered what a non fatty might look like until you mentioned it. I can see now where that might be a factor!
Oh yeah! 
The AM1000 has more chainline clearance than a
lot of ebikes; but in that lowest first gear (out of 11), the chain
almost rubs a 27.5×2.8" tire.
The chainring-to-chainstay clearance, looks like it'd
barely fit a 50 tooth chainring... or maybe only a 48.
48 tooth chainring to a 50 tooth first gear, would retain the same low gear ratio for climbing with the motor off (I ride with the motor off a lot), while allowing me to use last gear less often, & increase my range by contributing more pedal force at 20 MPH.
~ .... ~I'm off that 11t rear gear now, pretty much 100%. That was my primary intent, but I'd still like to go with a little bigger ring gear than the 48t. That's not going to happen until I have the need to replace some worn parts.
Amen to that! The bike works great once dialed in:
If\when something breaks,
then I might "upgrade"!
For now, it's lovely.
The
next bike will probably be first to benefit from my ideas for changing this one!
My thought on the rear cluster is that even my 9 speed is too many gears, even for the hilly area I run in. The Ultra is a huge torque monster. IMHO, there is no point in keeping it in a narrow rpm band or allowing for one if I did. If I were ever going to do a total rebuild, including shifter/derailleur, I would be more likely to go with a 7 speed. I don't need 9, and that would let me run a heavier chain as well. My casual start from a stop is usually done in 4th or 5th gear, while pulling 4-500 watts tops, and I climb most of even the bigger hills using 4th gear. So there's very little strain on anything. Point being, for my purposes, an 11 gear cluster would be way over the top.
I tend to agree: On the manual bike, I'm used to riding a 3× set of chainrings, with 10× cassette, so I was leery of losing too many gearing options, on a much heavier bike... but even 11 is far more than I usually need!
Sure, on the manual bike, I need every tiny shift in ratio, to get up to 30 MPH without huge jumps in effort; but I'll never pedal the
ebike to 30 manually, & with the motor, even 7% power erases any gaps in my personal power-band.
At low speeds, I'm literally shifting two gears at a time; I'm not using half the gears
at all! Larger chainring would make each shift cover a larger span of speeds; definitely worth it, if\when the cassette requires replacement too.
I don't want to change the chainring without the cassette though: 40t front on 42t rear, is just about perfect reduction, for crawling or climbing at low\no assist. I want an 11t-to-50t rear cassette, to match a 48t front chainring!
7 speed chain is surely tougher. If I start having chain breakage issues, that's the first change I'd make.
... but no such issues for now; & I suspect I'd like the extra gears, at low assist levels on rougher trails...
if the cassette were spaced a bit taller!
I am acutely aware of that; hence the desire for larger front chainring, to make use of the middle gears more! I don't like how often I land in last gear, even at low assist levels & long before "top" speed. 
The "Smooth" config was my starting point. 
