Gerunds

1.其實不論是否時間性介詞（prepositions of time）與否，其實所有介詞後面都要用名詞、動名詞，或名詞片語。
如：I look forward to seeing you.
　　He insists on leaving here at five.
　　He spends his spare time in reading.
2.其實你所見的是片語，片語是可以沒有主詞與動詞；但整句句子裏，除了你所見的片語外，必定有主要子句，這子句就必須有動詞與主詞。
　如：On hearing this, I changed my plan.
　　　On seeing me, he ran away.
　　　In spite of the sun shining, the air was cold.
3.其實動名詞的用法，跟名詞大若相同。
　　a. 作主詞
　　　如：Listening to music trains the ear.
　　　　　It is no use talking.(It = talking)
　　b.作補語
　　　如：His job is delivering newspapers
　　　　　Complimenting is lying
　　c.作為動詞的受詞
　　　I hate writing letters.
　　　The baby began crying.
　　d.作為介詞的受詞
　　　After seeing the play, I went home.
　　　He is capable of doing such a thing.
　　e.造複合字
　　　smoking-room，falling-sickness等
還有動名詞是有被動詞和過去時式，如：
I don't like being spoken to like that.
I never heard of such a thing having been done.

Answers to ur questions 1 & 2:

所有Prepositions 後都需加V+ ing
e.g. I'm keen on reading
I'm interested in swimming.
He talked without looking at me.
He passed the examination by paying a lot of effort.

3) 沒有補充