Use a set database schema or EAV design? I have already created a database design with a set schema.
The database schema is for a web quotation form. PS it is not a simple quotation form and hence need to customise the form, form builders like Gravity Form have been tried and suitable in this case.

I have about 15 tables (mostly in 2NF and 3NF) with set attributes and datatype.

But the question is should I stick with the traditional normalized schema design or use EAV design instead for some tables? It seems Gravity Form uses EAV DB design but that is due to the dynamic nature of a form builder.

This question has come up due to the fact that later on a attribute may need to be added, removed or updated from one or set of tables. The fields in the quotation form are reasonably standard with research done and I don't imagine modifying the fields and hence the attributes in the DB often.

I have read there are concerning pitfalls of EAV design. So if the fields are not going to changed often then is a set schema design with relationships useable?

Also in the event of modifying the schema is ALTER table going to cause any issues? If one adds a attribute to a table with ALTER table what would the previous data sets in the table have the value of the new attribute?
What are the alternative of ALTER table?
Well, wait until you see the ugly JOINs you will need.  I'm a strong opponent of EAV.  I have seen too many large EAV datasets groan under the inefficiencies.  However, since you have a tiny dataset, you might not run into the problems that others encounter.

Here's my blog on it, including one suggested alternative:  http://mysql.rjweb.org/doc.php/eav