蜘蛛先生，早上好！

Pretty good writing。

【1】 Sole我今天早上找到他 does not seem to be a complete sentence. As native Chinese speakers we usually use (是)...的with it. If you use 我今天早上找到他（它），you're probably implying you're continuing this sentence, i.e. 我今天早上找到他，（才知道）他已经把手机丢了。

【2】Using 还有 was not gramatically wrong, but not much of the Chinese way.  If you use 还有， you are emphasizing something important or surprising. [ But in Child language or, for example, lyrics, 还有 is possible here].

【3】和我的手一样大 is fine, and is possible from native Chinese speakers, but it's not so precise. 和我的手掌一样大 or 和我的拳头一样大 seems better.

他有八条长腿，还有八只眼睛。

他和我的手掌（巴掌）一样大。

刚看到他的时候我有点害怕，但是我知道他不会伤害我，他只吃别的虫子。