Upload all questions by tabular form (Excel File)

There are many questions, can I upload all the questions through the tabular form, then set the conditions?

No, there is no such a function in Survey Solutions.
See also here:

If there are many questions, I’m guessing typing them into a tabular file (Excel) will also take time?
plus, question is an object that has variable name, title text, type, answer options (for cat questions) etc, if a user is manually preparing such a file, she will need to fill out all this information - so again, perhaps not much of a saving from doing exactly that directly in the Designer app.

Moreover, in order for the ‘upload’ feature to work - the structure of such a file must be documented so that all users know how to prepare the file (which column goes the variable name vs title, how to refer to the Categorical: multi-select question type, etc etc) there must also be a validator that checks that uploaded file doesn’t violate the structure, and if there are mistakes, communicate to the user (show useful error messages in the Designer interface).

Would you elaborate little more how do you see the feature to work?

What about upload questionnaire via JSON? This could cover a few use cases–one immediately, another after some development:

  • Restore questionnaire to Designer from JSON. From HQ, one can download the JSON version of a questionnaire. But there’s no (user-exposed) way to create a questionnaire in Designer from that JSON file.
  • Create a JSON questionnaire from Excel. If the JSON schema is relatively stable, one could sketch a questionnaire in a spreadsheet and then convert that tabular format to JSON. This is an approach to questionnaire authoring that is very popular with ODK users. See more here, for example.

Of course, for this to work, one would need some mechanism to check JSON files for errors and message those errors to intrepid users who elect to create questionnaires via JSON. Also, Designer would (possibly) need to generate GUIDs for all objects defined in Excel/JSON.