New Bike Suggestion

Hello veterans.

I am 35 and I have been suffering from rheumatoid arthritis for the last 5 years. I didn’t do ANY biking between 25-30 but I did a thousand or two miles a year on $100 single speed road bikes and MTBs in urban and rural India until I was 25.

Now I need to get back to biking because I can’t drive and need a bike to go around Bay Area, CA for 10 miles a day, 4-5 days a week both on road and off when working and 5-10 miles to cafes on nice roads when I am not working.

Since I was in a rush, I picked up 6KU Urban Track for $299 on reading good reviews on its build quality and value.
https://www.6ku.com/products/6ku-urban-track-bike?variant=11809790853167
I am yet to open the box and assemble it. But to suit my arthritis needs (severe pain in wrist but not much at all in knees) I need to:

1) upgrade multiple parts in 6KU bike; budget for this is $400

or

2) buy a new mountain cruiser with fat tires or whatever category bike you kind people recommend to replace 6KU that I can gift to my neighbor’s kid. Budget for new bike of your choice: $800-$1000 (including upgrade parts needed as per your advice). Mind you, I won't be able to afford upgrade further or buy another bike in the next 2 years.

Please help me. I would like to do 1 or 2 but in the best possible way you think is right for my case.