Page 190 allows smaller jump jets on bigger mechs but reduced performance. Is the reverse true? Larger jump jets on smaller units having increased performance? For example, would a 2 ton Jump Jet on a 20 ton Singer provide 4 Jump MP?
No.
Would multiple larger jump jets act like Improved Jump Jets or would the Jumping MPs max out at the walking speed?
Max out at walking speed.
If the latter would those Jump Jets act as space in case of damage? For example would my Stinger with one 2 ton Jump Jet and two 1 ton Jump Jets have 8 Jump MP or 6 Jump MP with a 2 Jump MP reserve?
The excess MP potential is wasted.
Does the same apply when using Improved Jump Jets?
Yes, i-JJs would also waste MPs in the same way, and would be restricted to the 'Mechs running speed with regards to maximum MP.
It's not the intent of Frankenmech rules to create efficiencies not available in regular construction. If that happens, it's a flaw in the rules that should be corrected. You can use that philosophy when making decisions not covered by the rules, or answers in this forum.
Can Prototype Improved Jump Jets and Production Improved Jump Jets be mixed? Can they be mixed as above? Multiple sizes providing Jump MP up to the running speed?
No to all.
Can Standard Jump Jets and Improved Jump Jets be mixed? If yes, how would I determine the Jump MP? By adding up all the Jump MP or would it be limited?
No.
And if I used bigger Jump Jets would it increase that any or no?
No.
Would the answers to above also apply to vehicles when mounting jump jets on them?
Yes.
Are Vehicular and Mech Standard and Improved (both types) Jump Jets interchangeable?
No.
Would it be legal to mount Jump Jets in a Mechs arms as long as the mechs has the Illegal Quirk?
Anything is possible with the Illegal Quirk. Anything at all. The only limit is your imagination. /zombo.com
If yes, could my mech make a Jump Jet attack while punching?
There are no rules for that, but I trust you won't find it hard to make them up. You may want to check out the Fistfire SPA from ATOW as well.
Can Jump Jets be used to increase a vehicles ground speed? For example, can a Thorizer use it's jump jets as booster while on the ground?
No.