I have to throw another opinion here lol...
I'm a long time technical and marketing writer. Di's question really doesn't have a straightforward answer since she really didn't state the purpose of what she was writing. "I" statements are PERFECTLY acceptable if you want to put out your experiences and opinions in any setting or if you are writing biographical materials. For some reason, many writers feel it is being egotistical, but it isn't. You are simply stating your truth and putting it in your own words with the word "I" does lend your truth more strength. In other words, you are teaching the world about yourself and there is absolutely nothing wrong with that.
If she were writing procedures or policy for her company, then no... it's probably a bad idea to use the first-person point of view. Procedures and policy are typically written in second or third person. ("You must submit your expense report each Friday by 5:00 p.m." or "All employees are expected to be punctual.")
Or if Di were writing someone's memoirs, it would be unacceptable for her to state the person's points of view and experiences in first person, unless of course she were quoting them. That too I suppose would depend if she were ghost-writing them or presenting the material as a biography and weaving her own interpretations in there.
For me, I love it when I see writers put personality into their writing. I used to test newbie tech writers in a previous life. One of the tests asked them to write procedures on how to make excellent toast for breakfast. Mundane topic, but look at how it was modified, we "teased" the applicant's personality out LOL. Some of the BEST tests I got back from applicants were those who wrote them in first person ("I recommend you try honey butter on wheat toast because it's scrumptious.")
As for starting a sentence with "it," that is perfectly acceptable grammar-wise. I MIGHT edit you though if it were a vague reference within a technical document or a business document though lol!!! That would all depend upon the idea or the thought you wanted to emphasize with your statement. Saying "I am saddened" lends a bit different of a point of view and emphasis than saying "It saddens me that..."