This 姿 is modified by 芳江が泡を吹いてノビている, not ノビている alone. 姿 means "figure/picture/appearance", but it's often omitted when translated into English.
This 姿もある is simply "there is a 姿, too". The topic of your sentence is その中(に), which cannot "have" a thing. (A sentence like 彼女には夢がある is usually translated like "She has a dream", but it's literally "Within her, ...
「曲をかける」 means "to play a song/tune on the stereo/CD player, etc.".
In this case, the music is being played on the broadcasting system in a school during lunch time.
The music "reaches" the students while eating; therefore, it is described as 「かけてくる」 from their perspective, which becomes 「かけてきた」 in the past ...
It is not very natural.
It would be better, if :
- If you walk until you can see a green house, that is my house.
- If you can see a green house, then it is my house.
I don't know exactly why, but your sentence does not looks very natural in terms of native Japanese speaking. I feel after 歩って, there should be ...
Here's the breakdown:
ほっぽる: a colloquial godan verb that in this context means "to leave (alone)"
ほっぽって: the te-form of ほっぽる
ほっぽっておく: the te-form followed by the subsidiary verb おく, which means "to do something for the time being" here. See this question or this article.
ほっぽっとく: the contracted form of ほっぽっておく. See this answer.
ほっぽっといても: the temo-form of ...
Simply, this アニメ is the name of an old cat. うちの clearly indicates this アニメ belongs to the speaker's home or family. The の in 老猫のアニメ is an apposition marker (i.e., アニメ is an 老猫). See: What's the difference between 日本人の学生 and 日本の学生 ?