TSDZ2 setup recommendation

Hey guys i'm new to writing here, but been lurking the forum for some years now!
I've been reading countless pages in main TSDZ2 thread and i want to try it in my wife's bike.
She asked for electric bike, and i took the chance to DIY her bike instead of buying an expensive one!

She is 80kg and she will have a child seat with a little 2year old, totalling 100kg.
I dont want to go the bafang route, best is for her to actually exercise too so torque sensor of TSDZ2 is key here.
She won't be doing more than 20-30klm recreational , easy going rides at most. No mountain going up.
Bike is a 2021 scott contessa active MTB with 100mm front fork. Simple

Have come to the following setup conclusion:

Get the 36v/350w TSDZ2 and keep it stock with an old m365 scooter (10s3p) battery i have, and maybe create a 48v battery down the road and flash the firmware to work accordingly.
OR
Get the 48v from the beginning and make a 13s2p or 13s3p battery pack from scratch.
I think a solid 21700 13s2p will be enough for the type of riding and range we want it, and its relative cheap to make.
also like the stealth look of the battery.

Cost wise the first option is cheaper, maybe i could re-pack the 10s3p battery i have and make it a nice form factor.
Weight of setup and the stealth look are a plus for me. Big bulk battery packs are just not good to my eye.

You can run the 36 volt motors on 48 volts and are very good if you want a more free spinning motor using factory firmware. 48 volt motors have more torque and better suited to the road or riders who are not so proficient. With the OSF available then either works well.

Be a little careful with late bike frames, be aware the larger the tyre spec on the rear, the less chance you will be able to use a standard TSDZ2.

21700 13S2P batteries must have a 2C min draw off of about 40 amps, Samsung 40T are a very good example and we are using them with great success as you can get the pack to fit into quite a small top tube pack which you can mount on the bottle cage bolts.