> What is the Maximum observed variables can we used in the the AMOS (SEM) for one latent variable?

As many as you can fit on the screen!! Remember that big is not always better in the world of statistics, indeed the reverse is true. The art in statistics is finding parsimony, the right balance between simplicity and explanatory power. I'd prefer to have a small number of variables in my model rather than a larger number (if the models are equally good at explaining the data) as simple models MUST be preferred to more complex ones. Mark

Thank you for all your valuable suggestion. its very informative. Thank you once again.

Just go for CFA and then fix your items based on factor loading. No matter less or more.