Max load on a 30Amp Sub Panel
Well we don’t add breakers for the total. Your example a 30 amp feed with a 30/40/50 amp oven and a dryer would exceed the load calculations for a 30 amp feeder this is true a 50 amp oven alone would trip the 30 amp breaker if both elements were on.
But I could put 5ea 20 amp 120v  circuits  and be fine even with the total being 100 amps of 120, how could this be?
The actual load is what is used in the calculation and don’t forget 30 amps at 240 is 60 amps at 120.
Now to see if you can use some of your existing gear to do what you want.
Check the size of existing sub panel if it is 60 amp or greater it is likely you can upsize the wire and breaker from the main (I would keep the gas dryer).
if you go with a oven at 40a or smaller a 60 amp sub could do this with what you have listed with the gas dryer.
Where you could run into problems is the 100 amp main with gas heat dryer and oven 100 amps is a no brainer.
But convert these gas over to electric and your service will need to be upgraded here is an example of the ovens I have measured they run ~38 amps, dryers 24 amps and both of these are 240v loads so right there you are at 62 amps of true load, add another 13 for lighting and outlets (13 amps each leg) in this “small area” and you are up to 75 amps of load at that level most electricians would be adding a 100 amp sub.  Is the rest of your house only drawing only 25 amps? So with all you want sure it could be done and if you want to learn and your state allows it you can add the sub.
Many states allow you to even set your main panel. With code updates a new main panel that turns your existing main into a sub may be the best route, then pull from the new main or old main to feed the new area sub. Or sub of a sub.
Your question is quite broad and I tried to give you the info needed to decide if you can do it or hire it out