I've ABed a lot since a year ago and have lots of accounts and a VPN that's both dynamic and I can change the physical location of often.. suffice to say I've had a lot of experience. I've had dozens of accounts frozen for ABing over the course of 12 months, and the common denominator is that they had buy times under 2000ms. I've never had an account frozen when buy times have not dipped below 2000ms. I've also had accounts not frozen despite having buy times under 2000ms. The treshold might be closer to 1500 or 1700ms. But 2000ms has been safe for me 100%. Currently my avg buytimes are around 2200-2600ms.
Eating less (and eating the right kind of food) is much much much more effective than exercising! But do both! Just don't exercise and ignore diet. Good luck
This might help as a guideline for diet. If you just eat like usual for a day and then enter all of your food and diet then it will tell you which nutrients you have an excess of and which you are lacking, it's pretty cool!