The whole thing was really a small project- I'd say something like 'Though we started as a small project, the company has became one of the powerful giants in the field of aviation services though our continuous efforts.
rapid breath-taking + continuous insistence- here you're modifying words that don't really need modifying- if something is breath-taking, then I'd say there's no need to add rapid
wide chain of branches, agents- you have a chain of brances, but might 'network' be suitable for the agents? through a wide chain of branches, and network of agents (I'd also be tempted to remove 'wide' or use worldwide if it's international)
It has ever been our principle- this form is correct, but it's a bit rhetorical and I'd stick to 'always'
On the other hand,- I'd use what is more/in addition/ moreover, etc
dedicated staff whose members have considerable knowledge and expertise- dedicated staff, with their considerable knowledge and expertise
With the advent of 2006 which highlights our silver jubilee,- 2006 sees our silver jubilee
At last,- Last or Lastly
close working relationships that have tied us with our customers- close working relationships we have maintained ...
relationships and expending- expanding