I'd say the start of any business, when you need to take care of everything, 2-3 years were the hardest and most fulfilling as well because we got to learn and pivot a lot.
Treat EVERYONE how you would like to be treated. You never know who you're talking to, so treat everyone with respect, especially when you first meet someone new.
One of the hardest hurdles in business is managing all your responsibilities while not letting yourself get burnout on the job. A work-life balance is key!