The stats can be found in a few places, off the top of my head ARM mainhand = VIT, offhand = STR, BSM mainhand = STR, WVR mainhand = DEX, offhand = MND...
That's all I remember. Anyway, those stats only affect quality gain (supposedly) they don't affect durability loss or progress (supposedly) so it won't affect your success rate.
That may change with the changes to the way stats work in the coming patch (whichever one is doing that.) Generally just focus on getting good Control/Craftsmanship/M.Craftsmanship.
As for what level of leve is okay to tackle. This game is pretty bad at indicating what the appropriate level for anything is, so take a look at the item the leve is asking you to make before you accept it (eventually you'll memorize the rules for different types of synths.) Sometimes you may be R20 and the quest may say R25 (about 5 level difference is usually pretty safe if you've got decent gear) but the synth itself may be 28 with 2 skill requirements (like sheeting and glovemaking) If that's the case and you have neither, you're going to be SOL trying to make the synth (9 times out of 10)