They measure different things so they can't be compared.
A 1-amp adaptor can not be used for equipment that draws more than 1 amp. It is not clear from the question which part of your system is 12 v and which is 20 v.
Yes, only it will take the 1.2 amp a little longer to fully charge a battery than a 1.5 amp charger.
Yes, no problem at all going to a larger ampacity of wire. Larger size wire yes, smaller size wire no.
There no electrical units for measurement of volatage that are smaller than a volt. A millivolt (1/1000 volt) A microvolt (1/1000 millivolt) A nanovolt (1/1000 microvolt).
yes
Yes, you can.
20 amp on a 12 volt system
There is no 115 volt, 100 amp, or 400 amp switch on the dash of a 2008 Tacoma.
No. If you connect two 12 volt batteries in series(positive to negative) to make 24 volts, you will have 100 amp hours. If you connect two 12 volt batteries in parallel(pos to pos, neg to neg) you will stay at 12 volts but have 200 amp hours
A
Electrically yes it is safe but the pin configuration will be different.
Amp, Amperes is current. Volt, and any variation, is tension. There's no direct translation between them.