sensor size and telephoto

How does pixel density influence the resolution at super telephoto?
For example: Is it better to buy a:

1. Nikon 8800 with a teleconverter
2.Olympus e300 2x crop factor
3.Canon 350d 1.5 or 1.6 crop factor
4.Panasonic FZ20 with a 2.8/420mm x teleconverter?
5.7mpix consumer camera disassembled and lens replaced with a 35mm slr lens

Lens options:
1.Opteka/Exakta/Samiyang/Vivitar/whatever 650-1300mm f/8-f16 lens (1300mm
f/8 EFL Olympus) (teleconverter???) 250 Eur
2.100-400 f/5.6 with 1.4x teleconverter 500 Eur
3.80-200 f/2.8 Tamron or Tokina with a 3x Kenko teleconverter 600 Eur + 250
Eur
4.600 mm f/8 mirror
5.50-500mm f/6.3 Sigma with 2x and 1.4x teleconverters
6. A diy project of makeing the lens myself from components (found a front
lens 17cm diameter)
7. A telescope with an adapter 6 inch 1200 f/8 refractor 500 Eur + adapter

My goal is to get an image similar to the one from 20x50 binoculars or
better.
50mm lens is normal 1x, then 1000mm is 20x normal???

Thanks in advance.