6. I would use よく動きまわる.
7. 派手
8. Bicycle is 自転車, not バイク. バイク and オートバイ are completely the same. Also, weight is 重さ in this case. 重し is for a physical or psychological weight.
9. It should be 甘そう. 甘いそう is a hearsay.
10. If you want to use 何となく, 正しそう/気持ちよさそう sounds more natural. But, first of all, なんとなく正しそう/気持ちよさそう doesn't seem to fit as the answer to どうしてそう思うんですか.
12. I said "in this sentence". Your sentence is barely understandable in a context, for instance, 目の形は動物によっていろいろです。小さかったり大き かったりします。. You were talking about the "shape" in the first sentence, whereas you explained about the "size" in the second sentece. That's odd.