Having plants in the tank will help out with the cycling process.
As far as Stability. I've never used it as I don't really like to put any chemicals in my tank other than what's needed (dechlor). I've read of some people saying it's a complete scam while others swear by it. So it might be something you have to make your own decision on or research more.
To know that the tank is cycled, you'll need a testing kit. We here recommend the liquid kit to the strip tests as the strips are usually not accurate. If you can't afford the cost of a kit (they're about $25-$30 but last a long time and so worth it), then you can take a sample of your water to a petco, petsmart or maybe even your local fish store and they should be able to test the water out for you for free.
Here's a link all about cycling:
As far as the QTing plants, you can do a bleach dip and that would work to kill of any diseases.
Taken from a user at plantedtank.net (great place to find out some excellent information about plants!) "It depends on the plant that you are dipping. Some are more sensitive to others. You should use a 1 part bleach, 19 part water dilution (1:20). This is assuming you are using the standard 5% bleach solution." and a few minutes is all that's needed. Make sure to rinse them off after that really well.
There are fertilizer tabs, liquid fertilizers and things like that but it generally depends on what kind of plants you have. If they're easy, beginner plants...I wouldn't worry about fertilizing unless you're really having problems with the plants. I really recommend stopping at plantedtank.net and ask any plant questions you may have there. Or you could go to bettafish's parent site plant forum here: http://www.tropicalfishkeeping.com/aquarium-plants/