Preface: I'm new and still crap at this hobby, but I've done tons of research and asked a lot of questions. Hopefully I can give some advice based on what more experienced members have taught me. Everything I say from here on is my own opinion or somebody else's advice; I tend to talk like I'm dealing facts but for the sake of how much I'm about to type, assume it's unconfirmed info unless someone more experienced than me adds their +1
1) Boxwood:
These guys are really fun IMO. They are easy to take care of, easy to prune, and come in a lot of neat pre-bonsai-looking shapes and sizes. The major downside is that they grow slooooowly. If you're hoping to turn that boxwood into a thick-trunked beauty, be prepared to wait. A lot.
I only have one boxwood and it's quite similar to yours. I'm going to style it in a way that keeps it as short as possible because if I want to play the long game with it, it'll look ugly for *years* before it even resembles proper bonsai. I don't want to wait that long.
My nursery also sells more mature boxwoods with trunks about 1" or larger in diameter. If you want that size of a tree, my advice is to buy one that size. They're usually 4-6 times the price, but save you enough years of waiting for it to be worth it. At my place, your tree would cost me $15. The huge ones are $60. I'd rather skip eating out 3 times and buy the large tree than spend 5 years waiting for my small boxwood to become workable.
2) That second thing which I know nothing about:
I'm not saying you wasted your money, but to my eyes that tree has just about nothing interesting about it. I'd vote for letting it grow out so you have more to work with. I find it easier to cut back from a dense tree, than to plan for any of a million possible branch structures on a sparse tree.
When I see this tree, my mind goes to "try to develop an eye for potential bonsai material" because I would have skipped over that tree immediately after glancing at it. I'm learning more and more that while it's possible to make bonsai out of almost anything, it's really worth the time to focus on trees that have potential. It'll prevent mental burnout if/when the tree doesn't meet your expectations after styling. My first 2 trees were carelessly selected and I ended up hating them and wasting 60 bucks. One died and the other is sitting out of sight because it's embarrassing to look at. Try watching YouTube videos of bonsai enthusiasts hunting at nurseries. They usually browse and comment on why they like/dislike what they come across. It's really informational gold for us new hobbyists to be able to see the decision making process of these people. It'll save you money and heartache.
3) Set yourself up for success
My biggest revelation is the realization that if I can find out which species can take a beating and still thrive, I'll get a lot of enjoyment out of the hobby as I learn. My new favorite are azaleas. Cheap as dirt, beautiful flowers, and backbud like crazy. You can chop them as hard as you want and they'll put out growth like it was nothing. I currently have 2 of these. One was chopped back to a few bare branches, the other I left some sacrificial foliage on. They're both putting out buds. They're almost impossible to kill by pruning and you can learn a lot by experimenting. You also don't need to worry about which ones have potential before buying because you're likely going to chop most of the tree off anyway. I can't oversell how great those things are. Find what trees work well like that in your climate, and focus those.
Rant over
