Rules to my design of Alien

How would I start to design my own personal alien? I guess, I would determine the problems.

1. Weightlessness.
2. Distances that may far excide a normal life span.
3. Limitation of speed. Based on known science. Nothing can travel half the speed of light. I believe we can travel as fast as light but we need to avoid obstacles and this would limit our speed. Traveling light speed would blind the travelers. They would have to stop or slow down to decide directions to avoid obstacles that may appear in route capable of destroying our space ship.
4. Extreme temperatures.
5. Extreme radiation.
6. No limitation for size of transport.
7. Fuel limits. Fuel & Food must be collected or grown in route.
8. Light extremes. (Dark to Extremely Bright)
9. Building, construction or repair must be completed by the travelers. This includes mining for building materials in space.
10. Reproduction of occupants must be in route.
11. Size and number of occupants is dependant on available space and food without help from outside source.
    
    These are my rules that direct the design of my space alien. I may add more later as the need arises.