It's all down to expected power, ability to make stuff work and cash.

Keep the expected power output modest, find solutions to make things work together and it doesn't have to cost the earth.
Buy the best of every thing and pay some one to build it for you and you will need deep pockets and long arms.
Neither way is right or wrong.

The above engine complete and running minus trolley stands me at about £1100 give or take. I could do it for less if I made more and used less Rs parts and waited for a few more bargains.

That's engine, turbo, ecu the lot.

Expected power is around 215~220bhp. 250bhp with a blufin stage one map but this engine would be maxed out at that.

There are 101 different ways to do the same thing.