Professional services of any kind typically don't require much, if any inventory - because you are selling your time and expertise.

My personal experience in founding/running a business and mentoring other founders is that you will need both an interest in (bordering on passion for) whatever you sell - and decent business acumen. Without an interest in what you are selling, the temptation to offload the work will be high - and you will lose control of quality and serving your customers (hello, Boeing). Without business acumen, you will struggle to keep the business viable (mostly - there are a few exceptions out there). Also, get a good accountant to do your monthly books and taxes - they are worth their weight in gold.

If you are in the US, SCORE is a non profit of volunteers who either are current or former business owners. They offer mentorship to people wanting to start a business and are fantastic.

Finally, be aware that business ownership is high risk high reward, and a shit ton of work. If you are successful, you can be really successful. You can also lose your house.

Feel free to DM me if you have specific questions about getting started.