I did this about a year and a half ago concurrently with co-founding my 3-member rental LLC. My partners split the costs 3 ways with me and in return I've done the lion's share of property management to date. I pay all ongoing dues/fees to maintain the license and I keep all my commissions (after broker's cut).
It's worked out well for me. I turned a profit in my first year, which not everyone does, without doing any marketing or asking for business. I just bought property and collected commission every time. I also really enjoy, and feel we benefit practically from, having direct MLS access and the sense of being treated as more of an equal when working with other agents and negotiating deals. Look at the typical commission: the reason some people consider it exorbitant is that it pays for a lot of things they're not thinking about - countless hours and days spent on unpaid activities, clients who don't buy, thousands spent on marketing, etc. Acting as your own agent, you deal with none of that, and you still collect the same percentage. Or, you can offer to waive it as a negotiating tool, if the situation permits. It definitely adds options. Most brokerages will also give you extensive training and mentoring opportunities for no added cost - if you succeed, they'll get their cut at closing, so your success is in their interest too.
As noted above, make sure you accurately sum up the ongoing costs of maintaining a license. The fees are spread out between different rganizations and at different rates of recurrence, which I occasionally suspect is a ploy to get you to underestimate the total, but for me it's about $2K/yr. Total startup costs were about $2K as well.
Consult with a tax professional as well. Being a realtor can make you a real estate professional and rental homes are your active business, subject to FICA taxes and state business taxes that may not normally be levied.
Unless you spend over 750 hours per year (14 hours a week) doing real estate activities, the IRS does not consider you a real estate professional.
I have a friend who's an IRS auditor and we've talked about this a lot. I may not even qualify if/when I quit everything else and do it as a part-time FIRE job.
Not until you have tried being a LL. Try it for a year then decide.
That's really not a bad idea. I had been a landlord for years when I got licensed, and it was part of my push to expand and professionalize a small portfolio. I had also had years of peripheral exposure to Realtors, knew I wanted to be one, and understood many of the basic concepts already. If I had just been starting out, it might have been too much all at once.