As above. Parking is provided at Ellis Street. Bear in mind they will be bringing in an emissions zone charge in Jan 2020 for vehicles with high emissions however it’s only older cars and HGVs which tend to be affected (about 40% of vehicles). It wouldn’t surprise me if they change the parameters within the next few years or even follow this up with a congestion charge zone for the city centre much like London.
Just to expand on this - for private cars to be exempt, petrol cars need to be Euro 4, diesel need to be Euro 6. Plenty of newer diesels are Euro 5 so will be affected (think the shift to Euro 6 was 2015-2017 depending on manufacturer.)
The scheme is largely identical to the new ULEZ zone in London, therefore you can check your vehicle here -->
https://tfl.gov.uk/modes/driving/ultra-low-emission-zone/ulez-vrm-checker
If it passes for London, it'll be ok for Brum. I largely agree that the parameters may shift in a few years, but I don't think it'll happen for a while as a lot of people have now upgraded to Euro 6 diesel at some cost on the back of what the council have implemented.
I'm also led to believe that if you pay to enter the zone that's valid for one calendar day, not 24 hours. So if you started work on Monday at 19.00 and finished at 02.00 you'd end up paying twice.