Does it a good strategy to lose five pounds in the first week of a weight management plan?

No. Healthy weight loss is generally considered to be weight lost at a rate of about 1 - 2 pounds/week. Weight is easier to keep off when lost at a slow and steady rate using a healthy diet and exercise regimen that can be sustained as a lifestyle, rather than a crash diet. The best diet is one that you can stay on and maintain for life.
Yes! But ..... For the first week of a lower cal, lower carb menu you could easily lose 5 #s- attributable to some water weight loss. Afterwards we try to shoot for 1-2 #s a week for healthy weight loss goals.