Possibility over tightening the tension, set screw needing adjustment, blade allignment out, too much force on blade while cutting, stock thickness, speed, wrong blade type. Just a few thoughts re: blades breaking.
I'll study an intricate pattern prior to cutting so I'm aware ahead of time of some of the issues that can arise. Once I've planned a general route visually which only takes a few minutes I than give thought to other considerations. Such as blade type, backer board, tape and etc. This training of thought soon becomes automatic and before you know it you're challenging yourself to more intricate patterns.
When it comes to any fragile area to be cut I use packing tape to help give it more strength.
You've done an excellent job cutting Bob. Well done. If you altered a branch a little, then it was meant to be ... right.
Any orbital sander will work Sam. It's a matter of preference and budget in mind. Majority of them are made in China and chances are from the same factory with a different name and casing. I happen to use a Makitta but have used Craftsman as well. No difference other than price. I hook mine up to a shop vac being I find the dust bag useless.