I'm at a slight disadvantage as I can't see the images (at work) but can imagine from the descriptions (Forgive me if I'm wrong but I'm presuming it's a 30mph limit?)
Glad you and the bike are relatively ok.
Have you got a copy of Cyclecraft?
Accident stats apparently show most collisions between cars and cyclists happen at the 'entry' point (70%). My commute takes me across several and I'm always extremely cautious. Being able to say "I think you'll find I had the right of way" is not much of a consolation when you're led on the road
Position: I'd go with Cyclecraft which talks specifically about the advantages of not taking the outermost (left hand) course but rather keeping to the middle of the left hand lane. After that it depends upon speeds and volume of traffic.
Observation: You need to get eye contact with every driver at every entry point and make sure as far as possible that they have seen you before you commit to passing them. If they are approaching the line, not slowing and on a 'collision course' I'd slow and wait to make sure they are going to stop before passing them. This does create an issue though as some will treat that as an invitation to pull-out, even if they have seen you. Which brings me to..
Speed: entry and 'in' the roundabout itself. It's interesting that some consider 25 mph too fast. In lots of circumstances I deliberately set out to carry as much speed as I can through a roundabout, especially if it is 'free and fast flowing'. Taking account of what I said above about observation. It discourages following drivers from 'cutting me up' (ie. overtaking on the roundabout and cutting across my path to reach their exit).
Final point: watch out for diesel spills, especially in the wet.
Oh, and on 'making yourself seen' it can help but I've still had drivers claim "I didn't see you" (meaning I wasn't looking) and I wear a white helmet and hi-viz jacket, have you thought about running a flashing LED light during the day (the one's that MartinE is so keen on!).