Hey Op,
Don’t be put off, I was not far off your weight and a self built ebike really helped me. I am now down to 138 and starting to really enjoy long rides and using more of my own power. You will need to spend wisely and buy good quality components but they do take the weight.
My bike below can really take the weight and the setup is not that expensive. Another route to go is using a Dutch bike frame as they are built like tanks.
For the frame I went with a good steel cyclocross from Surly. It has taken some abuse and has been sold, I picked mine up for under €200. A good quality touring frame would also work.
For Wheels any good quality 32 spoke would do the job, at first I did pop a few spokes but after I got them re-built at my local shop I have not popped a spoke and its been really reliable. Get chunky tires and pump them up high, I have 32’s and take them to 80psi when they are rated for 50/60.
A decent MTB groupset with high gearing is a must, I use a mix of Shimano that I mostly picked up 2nd hand. It’s a mix of deore & XT
Motor - I have bafang mid drive that is 750w rated that I ordered from Greenbike Kit, this is paired with a 48v battery and has never let me down and pulls me up any hill or trail. With the gearing I have and the fact it is mid drive it is never under serious strain.
Brakes- I originally used the brake levers that came with the motor kit, with my weight they didn’t stop well so I ordered a brake sensor and now use decent shimano leavers.
Saddle - I tried loads and with our weight I would highly recommend a brooks B17. Anything with padding will just hurt you.
The build came in under €1600 and has plenty of performance, I would NOT fit throttle as I got lazy so I have taken mine off and its pedal only now.