Assuming you have the multiple entry stamp, no restrictions. I've visited Vietnam twice, Cambodia twice, Singapore and Philippines, and 4 trips to the USA with no issues.
Others have provided the cost; I will add that it took me with my agent about half a day to get everything done from start to finish. A great solution.
You are absolutely on the right track to get an agent to take care of all this. I used an agent for my initial retirement visa as well as my renewal and the 90 day reporting. I place a high value on my time and convenience and this way it got done quickly. BTW, my agent is out on travel otherwise I'd pass along her info.
Great answer: Retirement Visa is reliant on myself which is 100% iron clad. Anything else would be sketchy; not wise to have your future controlled by someone else.