I also vary the price a lot and VERY REGULARLY, although only since it's slipped from the charts. Varying from £.59 to £2.99. You might be surprised at the effect this has... The higher price tends not to affect the number of sales too much so I try to keep this as high as possible.
The second app is a little more niche. The only advertising (after an initial flurry of tweets) has been via links on my website (just for promoting my freelance work) and the website of the content owner.
So... A) 2 B) both paid C) see above D) £2500 - £4000 per month