Those ?'s should be answered first, but you are probably going to have to mix up your salt water the same way, but add a little more salt to your mix. Do not adjust too quickly though. I say maybe half of a point per week until you get it to where you want it. Then when you are making up your SW mix for water changes, you'll have to adjust a little bit the amount of salt you put in. I find about 1/2 cup of salt per gallon will get you around 1.021-1.023 depending on the salt you use. To go higher than this you need to add a little more salt. How much are you making up at a time? How often do you do water changes?
just keep adding salt but you shoul make a bucket of freshly mix salt then add little by little if you drip add that will be better to minimize the fluctuation also you could do water changes with a little higher salinity than your tank water (take it slow)
Just use normal saltwater for topoff.
Using high salinity water for a water change is too fast and you also run the risk of precipitation while mixing up super saturated saltwater.