At first, in the start, at the start/beginning

[Wai_Wai]

At first, in the start, at the start/beginning
Q:
1. At first, initially, originally, in the beginning
Usually "at first" is used to describe the following situation:
When it begins, the situation is such-and-such. Later it turns out to be a contrast to the beginning situation.

I would like to know:
- whether it is a MUST that the beginning situation has to be the contrast of the later situation. (eg At first I liked the girl. Now I still liked the girl. Is it grammatically correct?)
- if so, do other words such as "initially, originally, in the beginning" have this requirement?


2. In the start
Does such a phrase exist?

3. at the start/beginning
- is it true we MUST use it like the following structure?
at the start/beginning of something

- is it possible for me to use them in the sense of "at first"?