The meaning of 'might as well' and the problem between 'risen' vs. 'rising'

the meaning of 'might as well' and the problem between 'risen' vs. 'rising'

The passage from a book, Cooked: A Natural History of Transformation By Michael Pollan.
https://books.google.co.kr/books?id=be2XOQ2sB_EC&pg=PT214&lpg=PT214&dq=Still+wearing+oven+mitts,+I+tapped+on+the+bottom+of+the+loaf+and&source=bl&ots=u32OD0k4gn&sig=CdFtqTBi7QINeNENY5N8UpiXtS4&hl=en&sa=X&ved=0CB4Q6AEwAGoVChMIp8Phr-mqxwIVgSqUCh2bRgQQ#v=onepage&q=Still%20wearing%20oven%20mitts%2C%20I%20tapped%20on%20the%20bottom%20of%20the%20loaf%20and&f=false

I held the loaf up to my cheek to feel its radiating warmth. ... I hadn’t done much, after all, except mix together some flour, water, and a little sourdough starter, and then treated it like a baby for several hours. And yet — here was this substantial thing that hadn’t existed before, this fragrant risen form. I might as well have pulled a rabbit out of a hat, and indeed my family, whose expectations for this latest project of mine were modest, reacted as if I had.

In this passage I have two questions.

First and foremost, the meaning of the underlined 'might as well'.

Usually 'might as well' has a meaning as follows:
http://dictionary.cambridge.org/dictionary/english/may-might-as-well
used to suggest doing something, often when there is nothing better to do:
? We might as well walk there.
? We may as well start the meeting - the others will be here soon.

But in this context in question, it sounds different. However hard I may try, I cannot figure out the meaning of it.
Can you give me your answer and, if you can, another example sentence?

Last but not least, the underlined 'risen' gives me another headache.
To me 'rising' seems better than 'risen' and 'rising' seems to be better aligned with 'radiating' stated before. But I cannot find out any ground supporting my argument.

(I know I can post one question per post. But these questions come a sentence after another. So I post two questions. If there is any problem, you can answer me first question.)

Regards.