Spacing and indentation

Spacing and indentation

I have this code example:
\documentclass[]{article}
\usepackage{amsmath}
\usepackage{amsthm}
\newtheorem{exmpl}{Example}
\begin{document}
\begin{exmpl}
\textbf{My first grammar}\\
$G = (\{a, b\}, \{A, B\}, S, P) \: where \: P:\\$
\begin{flalign*}
& A \rightarrow a&\\
& B \rightarrow b&
\end{flalign*}
\end{exmpl}
\end{document}
This ends up as:

I want to modify my code as follows:
There should be some more vertical space between the line starting with
"Example" and the line starting with "G = ".
I want less space between the line starting with "G = " and the following
flalign. Maybe just a normal line break.
I want to indent the flalign environment a little bit.
Any hints on this? Thanks :-)