Tie them as soon as they are strong enough to take it. Use thick yarn or bits of cloth. Tie loosely.

Be wary of pests going outdoor to indoor. Isolate and treat them for bugs so they don't contaminate your grow area.

No. Do not mess with the photoperiod unless you are using timers to do it, such as in a greenhouse, where you won't forget to move them that one night you are stuck late at work.

It is done, but easier to take clones and establish them in hydro from the start. The switch is going to be stressful and difficult, and the soil on the root system will tend to clog your system.