The more I look at, the more I found that I'm in a serious lack of knowledge.
TTL outputs are of 0.4mA at best, so it won't even be enough to drive a typical relay which takes 30-50mA! So, I will need to use a L293D eventually. Question is, it seems to me now that a L293D might not give enough current do drive a geared DC motor (I saw it once or twice from some tutorial websites), so maybe the final solution is to use a L293D to drive four SPDT which is then to push two DC geared motors.
However, I'm still puzzled.
Some of the shelf kits are available, but their what and how are still a bit cryptic to me. Shall still carry on the investigations.