Rent below 30 days (a'la AirBnB) is illegal as it competes with hotels. There may be large posters at the condo entrances stating just that. Neighbours could report you and get police to harass your tenants, drag them to police station, etc. Google up stories from C condo in Ekkamai to see how that looks like.
Long term it is allowed to rent but there could be restrictions put in place by the condo committee. In general the focus would be on not allowing any activities that would degrade the value of the units of condo owners. Our condo has smoking on balconies banned with fine for every report.
On the flip side, if it is a longer term rental, juristic office handles everything. They check the person in, do the reporting, arrange cleaning, room inspection, handle payment, even advertise property and show it to potential tenants. AFAIK they don't charge for that.
Finally on taxes - as you're private owner, you were supposed to add the income from rent into your annual tax report under other earnings, then pay tax on it per progressive scale. Given the size of unit, if that was only income you had, you'd not reach any tax even you rented it out the whole year. But I don't know what other complications that can bring as you would have income in Thailand... obviously you would need tax ID but would there be any other consequences? Don't know.