You are doing well. I trust that you will be able to get back to low carb again after the 'festive season'.
Exercise is important, but apart from the bare minimum it's less important than a good way of eating is.
The NHS advise exercise is (only) a brisk 30 min walk 5 times per week (or shorter amount of HIIT).
If you want to do more exercise than that, then it's a good idea to make it muscle building (in preference to cardio) because muscles absorb glucose from the blood stream.
I will not comment about the current figures you quite, just on those for April and August.
1. Trigs - a vast improvement. No worries hear if you get back to low carb.
2. HDL - I'm a little surprised that this hasn't increased on Low Carb. Are you a vegetarian? Do you eat enough fats?
3. LDL nor surprise and this wouldn't be a concern if only your HDL was responding the way that most does for most on Low Carb.
4. I'm not sure which ratio you are measuring here. The commonly quoted ones are Trigs divided by HDL or Total Cholesterol divided by HDL. Or the inverse of those. Anyhow, as I have said your HDL could do to be higher and if it was everything else (lipid wise) would be looking much better.