In my page body, I need to insert this code as the result of an AJAX call:
Loading jQuery
$.ajax and $.load are the same thing. You can use either. If you put $.load in a script tag on the page it will fire when it loads just like $.ajax().
When it comes to waiting for a script to fire before you do something what Tomalak said is kinda true. The exception is asynchronous calls. Javascript will make an AJAX call then continue running the script and when the AJAX call responds it will run the success/fail depending on what you tell it to do.
Now say you want your JS to wait for the return, with a single call it's pretty easy just wrap every thing in the success callback, or you could do it the cool way and use $.deferred. This allows you to make a bunch of ajax calls or one and then run some code only after the finish.
$.when & $.then are probably the best for this situation.
Any way what your are doing is safe.