Is there a speed limit for airplanes?

Yes. Jet packs do exist.

The type rating is required in aircraft that need additional training. It is a safety of flight issue not a for hire issue.

Usually it is airspeed of the aircraft. Each aircraft has different airspeed requirements for operation the flaps or landing gear. Usually that speed is determined by the airframe manufacturers and the design of the flap system component. You could built it strong enough to handle any airspeed, but a plane can only carry so much weight. If you built everything to work without any limitations you might have an airplane too heavy to fly. Designing a plane is a balance between lifting capability and weight. Both of these are important design parameters.

Your question is a good one - but the answer is much more complicated that you would expect. Think about driving your car from point A to point B across a city. Lots of paths - some shorter than others, but the shortest path may not be the quickest. Or the quickest may involve a toll road - and you may or may not be in a hurry.

The usual most important factor (for commercial operations, at least) is to save money, while still arriving on time. Airplanes in the air are subject to the winds aloft, which will generally be at different strengths AND DIRECTIONS at different altitudes. Most airplanes operate more efficiently at higher altitudes (up to limits), but at those higher altitudes the plane may face stiffer headwind. Further, it costs time and fuel to climb to those altitudes, and you will not regain coming down as much as it took going up. [Think of a bicycle on hilly terrain vs. level ground.]

So what's the answer? Well, for most trips the pilot will consider all these factors. They are taught during training how to plan the flight in terms of time and fuel required, and to include in that especially the winds at different altitudes. Then they will pick the altitude, whatever that is, that maximizes the results that they consider most important.

Many of the current general aviation planes now come with a ballistic parachute from BRS.

That would be the ground prox system on the aircraft it lets the flight crew know how far they are above the ground during an approach to the landing runway.

amid is Russian

Aircraft too heavy. Weight is extremely valuable/expensive and the weight of a parachute system would be too heavy and costly, sacrificing room for paying passengers.