You' ll need a
base cabinet for oven
then a
countertop
and a
oven (there's a typo : these are all 24" x 24" x 24" ovens)
then a
gas cooktop

It is the same as you had a 24" dual fuel range : you' ll have the gas supply and also a 220 V - 15 A line for the electric oven. Maybe I'm wrong .... don't guess one needs any permits to have a further electric line, it has just to be routed according to local codes

Whether or not you need a permit to add an electical line probably depends on your locality.

Dedicated line for which one? The gas cooktop or Oven? Most ovens are 240v and most codes require a dedicated circuit/breaker for such an appliance. The gas cooktop likely needs just a 120v recepticle. They manufacturer may tell you it needs to be dedicated but as long as it is not on a GFCI you will probably be okay sharing that circuit. If it is on a GFCI the sparkers may trip the GFCI.

Most electrical codes require major electrical appliances (such as ovens, cooktops, clothes dryers, etc.) to be on separate dedicated circuits. For a single oven, you will probably need a 220V-240V 30 amp line. The cost for installing the circuit will depend upon the distance of your kitchen from your electrical panel, whether or not your panel is sufficiently sized for the additional circuit, and the ease or difficulty of running the line from the panel to the oven location.

Your best bet is to seek several estimates from different electricians for the job. If the estimates are all similar you'll have a good idea of what the project will cost. This type of project nearly always requires a permit and inspection by your local building department.