I'm going to suggest wrapping some of the formulas in an IF statement. Specifically the formulas in columns B, D, and I.
In column B, I'd suggest using
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=if(A2="";"";A2-A1)
This is a simpler method of calculating the number of days, which is what the DAYS function does, and it takes into account if the current row has an entry in column A or not. You can enter the above in B2 and then copy it down for however many rows you feel are needed.
You can also copy that same formula over to column D and column I, as the reference points will adjust automatically.
This will handle most of the calculations I suspect that you were wondering about... others will become a 0 or updated as the required information is entered.
You do have two columns with static data entered, which I have not touched, though looking at the data makes me think that these could be changed to a formula so that the previous entry is used, rather than a static entry on all rows... by changing them to formulas, they could be wrapped in an IF function similar to the one shown above.