Well, it certainly looks ok, I am glad you nailed it. 30 mins may be a bit overexposed as you said, considering that there is no paper base white , but I believe that is personal matter of choice.
Loris is very right, some sort step wedge is very very useful to determine correct exposures, it would save you from a lot of trouble.
BTW I want to share my experience with brushes, I feel that the brush will always cause contamination, black dots, irregular densities, distracting patterns and so on, no matter how careful you are.
A glass rod/puddle pusher is perfect for Salt print. If you decide to include gelatin in future, a glass rod would save you from lots of troubles.