I’m a firm believer in there being no such thing as a stupid question but it can be stupid to not ask one.
Regarding the category for Gross Pay: There should already be a default entry for this but it might be called Salary or something else. I've modified my category list so much that I don't recall what that default is. The best thing is to pull up Category List (under Tools) and then click on Personal Income on the left so only the income categories are shown. Then sort it by clicking 2 times on the Tax Line Item column header so all the tax line categories show up at the top of the list. Review the W2 tax line item categories and use the appropriate one. If you don't like how that category is named (i.e., Salary), you can edit it to change its name (i.e., Gross Pay) by clicking on the category to highlight that line and then clicking on the button in the Action column on the right. You can create a brand new category for this if you wish but that is a little more involved and it really provides no benefit over simply using the default category.
Regarding the split category entries:
Since you created a new account just for your W2, here is another option you might want to consider: Instead of doing a single split category transaction you could do multiple transactions in the account register, one for each debit and credit and each with the same 2019 transaction date. When you’ve accurately made all your entries the ending balance in the account register will show $0.00. The main advantage of doing it this way is that you can then see each of the transactions directly from the account register without needing to take the additional step of also clicking on the split category. You might also find it a little bit easier to make any edits to fix any errors you might find. In addition, in some reports (where the data is not filtered by category) the details of each of those transactions will show up individually instead of showing as a single split transaction of $0.00. In the end, entering this way or via a single split category transaction is just a matter of personal preference.