In addition to those already mentioned, consider taking Sudden Still, as it makes a useful once-per-day "get out of jail free" ability if you find that you need to use an invocation whilst grappled or otherwise restrained.
If you go with Point Blank Shot and Precise Shot, consider Improved Precise Shot at 15th or 18th level.
At higher levels, after you gain access to Greater invocations, the Extra Invocation feat becomes worthwhile, to gain access to an extra invocation of Lesser level.