Whether your data is too large depends on many things, such as the memory of your web server. The best way is to use Session to test performance. If you find that your data is too heavy, please see Look at the ASP.NET Profile.
I am doing a survey builder, and I want to use a unique guid key to store the survey in the session until the user completely creates it and Save it I think it will be an array containing 100~200 objects (8 attributes) class)
This sounds like a reasonable use of Session.
Whether your data is too large depends on many things, such as the memory of your web server. The best way is to use Session to test performance. If you find that your data is too heavy, please take a look at ASP .NET Profile.