The waters are quite safe, just watch the wind and the tides
There is a zoomable chart you can study here, an excerpt of which is below:
The key thing you will note is that you want about 1.3m of water to avoid trudging through the mud at Cleavel Point, nearer 1.9m if you wish to make it into Newton Bay - the ground at the tip of the point is much less muddy!
The tides can be found here, just change the Daylight Saving to 1 hour and the Max. Graph size to one day, then press 'Apply' - this is set to Cleavel Point.
If you are wanting to head to Wareham on Friday night, use this tidal info for when you're at Wareham Quay - give or take, Wareham is about an hour behind Cleavel Point and will take approximately 2.5-3 hours to paddle back from.