You are going to get several different opinions on choices based either on brand loyalty or outright experience . You will need to do your own homework as to whos opinions are worth your time and in vestment including my own.
The best advice anyone can give you is don't buy anything just because it is the cheapest especially servos . See what people are using successfully and then see if it fits your budget.
With regard to an engine 30 to 40 cc range the dle 35 would be my choice
With regard to servo you dont need anything fancy, digital is not necessary but is nice to have . I would go with Hitec 645mg or 5645 mg digital both are reliable and relatively affordable. I cant give an opinion on a mechanical retract servo but Hitec probably has one to fit your needs as well.