Here's a simple test to determine your optimal carb intake. You should perform this test doing the same level of physical activity you plan to do after the test. You'll need to adjust upward or downward if you add or increase your activity level in a big way.

STEP 1: Go for a week (or ideally two) with no additional carbs except naturally-occurring carbs in Fibrous Vegetables (see Carb Type Strategy). You will either feel great, or pretty miserable. The next step tells you what to do.

STEP 2: Gradually add carbs back into your diet. Start with Level 6 carbs, and work your way down. Spend 2 - 3 days at each level. (Note that the impact of carbs varies depending on how you eat it - see below).

If you were miserable on low carb, eventually you'll start feeling better. When you start to feel better, that's a good level of carb intake for you.
If you felt great on low carb, you can either leave it as-is, or gradually add in more carbs until you aren't feeling good any more. That's your upper limit of carb intake.

NOTE: Adjusting to ketogenic levels often requires a 2- 4 week adjustment period where it's normal to feel somewhat miserable as the body adapts to using fat instead of carbs. However, for anyone who is a perfect fit for the ketogenic diet, they are more likely to have minimal symptoms or feel great more quickly. For people who are better suited to carbs, it this test may be done in reverse: gradually eliminate carbs starting at Level 1 until you feel like it's too restrictive.

How to Eat Carbs While Reducing Blood Sugar and Insulin Problems

There are ways to eat carbs while minimizing the impact.

Two suggestions:

Avoid eating carbs alone -- instead, eat along with adequate protein and/or fiber and/or a small amount of dietary fat
Spread your daily carb intake over multiple smaller meals (without increasing your total daily intake)

Doing either of the above, you could "get away with" eating refined carbs (sugars, bread, pasta, etc...) more easily. It effectively lowers the Glycemic Index (GI) because a large amount of glucose isn't hitting the system; digestion is slowed. The fiber content of whole fruit is why whole fruit has lower GI, but fruit juice has a high GI. You can also handle refined carbs more easily if you eat it in small portions (easier said than done of course).

Another way to reduce impact:

Avoid all refined carbs -- instead, choose whole food carbs
Eat at Level 5, 6, or 7 to dramatically reduce or eliminate any problems

What About Sugar Substitutes (Artificial Sweeteners)?

Some people suggest that sugar substitutes are bad, claiming they cause people to eat more food and/or cause hunger. However, research doesn't support that assertion so you should feel free to use them. That said, you should be careful and note how sugar substitutes affects you personally. If it triggers cravings for more or seems to sabotage your goals then obviously you should avoid using them.

Also, you have to look at all the ingredients in anything you're eating, particularly packaged food. Just because it has a zero-calorie sweetener doesn't mean it's not an overall high calorie dense food due to other carbs or fats.