Hybrid bike: What model to choose when buying a new bike?

Hi!

Planning to build a bike for myself and would like help for choosing the right bike. New e-bikes in Europe with decent quality and mid-drive torque motor start at 2500 Euros. Would like to find someting cheaper and being able to build it myself sounds both fun and I can easily change motor/battery in the future if needed. 

Since I dont have a bike and have had no luck in finding one thats used and meets my requirements I guess I need to buy a new bike and convert it. 

I would like a bike:
With quite upright seating position 
Thats good for riding both asfalt roads and gravel roads and sometimes paths in the wood
That has hydralic discbrakes and shock absorbers
Budget and basis
Approximately 1000 euros/dollars for the bike +/- 2000. Additional 800 for the Tongsheng motor with torque sensor. 
I am quite long at 190 cm so need a XL size
With all options open what would you have done? Is it even a good idea to first buy a brand new bike and then convert it. And if so can you recommend a brand and model thats great for conversion for my needs?

I was looking at Scott Sub Sports. But those bike models have 24-30 gears with 3 front wheel gears. Better search for a bike with hub gears? 

Any ideas most welcome!

I like older bikes with large triangle frame for big battery. Such as a kona or giant trance. Think how big a battery you need and how far you need to go and what hills to climb ? Where will the controller be ? What display. What country do you live ?