Cycling a brackish tank that will become saltwater?

[Crabcake]

Hello! I need a bit of help here.

I have been a fishkeeper for 3 years, and I have a green spotted puffer in a 10 gallon who is in a brackish tank. Since he was so little, I didn't cycle the tank before and just did tons of water changes and he was fine. I will be moving him to a 29 gallon now (he's about 2 inches) and was wondering how I should cycle it.

As some of you might know, I will have to transition him from brackish (he's in about 0.012 right now) to marine (around 0.022 or something). I saw from other forums that as the salinity changes, the bacteria die off because they are not "the ones" for that specific salinity. So would it be a waste of time to cycle the tank if the bacteria is going to die eventually? I am thinking to raise it about 0.001 or 0.002 per 1-2 weeks. I'm still going to do like 20% water changes weekly and have an aqua clear 70 in his tank.

Will he be fine? Thanks!

I also have one more question. It is about the "python" vacuum cleaner thing that's expensive. I know it can be used for freshwater tanks, but for brackish or marine tanks, how will it work when filling it up with water? Won't it make the salinity lower, causing some bacteria to die and the fish being stressed? (As you see, I am a newbie in brackish and marine, haha I only did freshwater before).

Thanks! Anything would help!