1. There is no such thing as 'Bonsai seed', or 'bonsai tree'. It's all in the care, pruning, rooting, and potting. Almost any sort of plant can be 'dwarfed' and appear as 'Bonsai'. Some species take to this more naturally and appealingly, than others.
2. Bonsai do not thicken well in pots - they must be allowed to grow unconstrained in the ground to reach appropriate trunk thickness. Chopping, develops taper. You will own more 'trunks' far longer than you will have finished bonsai if done properly while enjoying this Zenful practice. Think of it as 'tree farming'. :)
3. You 'can' replant your Mallsai (Those $20-$40 glued-in-stone creations from 'large' garden centers..) in the ground to regain trunk thickness - but will lose some existing natural Jin in the process. (A positive in my mind)
4. You don't have to go find a 100 yr old tree, to find good material. (It likely will be though)
5. Not all trees, are good material... :)
6. Don't let the bonsai addiction keep you pinned to small beginnings - go find a mature bonsai that you like, bring it home, learn how to care for it; watering, pruning, repotting. You will learn much from the care of a mature bonsai. As you grow your 'sticks' and captured 'yamadori' into future Bonsai, this knowledgable care will be passed on to your expanded collection.
7. Don't toss your 'sticks' out once you realize that's what they are - everything has it's place (not necessarially in the compost heap). They are great to develop 'habits' of tending and care. You might develop a nice looking tree out of them yet - with time and patience.
8. 'Do' invest in some unique species seeds if you have patience and time. This does allow complete control of the plant, especially it's taper in early stages. Just don't plan on calling it a bonsai for at the minimum 5-10 years. (It it's more than an addiction and is a passion - you will want a few like this in your collection at some point, to expand your species and available material for future trees).
9. Bonsai do not, live well inside, no matter what they tell you! Only a few species do ok in the home, and even less 'thrive' inside. Plan to give your trees good viewing locations outside. They are to be viewed and enjoyed, their energy felt! Our natural tendacy is to bring that inside with us - give them their world, and that is outside. Visit and tend them, in their world and you will be rewarded by their presence.
10. Create what you like, do not lock yourself into 'style' standards. It's good to seek opinions from others, share your work and gain input. Do not let it turn you off or hurt your Ego to hear hard truths about trees. In the same vein, take it all with a grain of salt; many bonsai masters or 'sculpters' think nothing of their comments, or the original design of the bonsai owner themselves when they review a tree. Many hold strict standards, while others have such high marks that an honestly beautiful tree may hear nothing more than 'looks ordinary'. That's great! Bonsai should look as regular trees - not all have to appear as if they are balanced on a cliff dangling for their lives. :)