Machines are wack. Good thing you don't have them. It seems like you have a good progression for your dips and chins. If that's all you're doing right now, then you could continue to do so until you feel unmotivated, see no improvement, or feel burned out.
At that point you could switch it up a bit. If you have a barbell and some outdoor training equipment you could try CT's Renaissance Training (with dips, chins, and deadlifts in the weighted portion).
Other than that, I think the ladders and GTG are great for increasing your repetition numbers.
If your goals are to increase your limit strength on these exercises, then you could try a Westside Approach (WS4SB).