I'd have to agree there is a chance of oxidation anytime you transfer and the extra headspace of a bucket especially a 7 gal. bucket would slightly increase those chances therefore if it were me I would transfer as soon as the fermentation started to slow down. That would give the yeast a chance to build up a protective layer of CO2 right on top of the beer.
With regard to scratches in the plastic bucket those can be prevented simply by soaking the buckets in warm or hot water and oxiclean or Automatic dishwashing soap for 24 hours then rinsing. Don't scurb the bucket or if you must use only a very soft rag.
As far as the oxygen permeablitiy of HDPE buckets I don't think I'd age my beer for 2 or 3 months in one, but I don't need to because I use corny kegs for secondaries, but I wouldn't think a couple of weeks in a HDPE bucket would make any difference. And I've never read of anyone saying they have personnally had a problem with them oxidation wise.
I do believe that a carboy would be a better secondary than a bucket as long as the beer is protected from light. That's why I use corny kegs as secondaries they cost about the same as carboy's but you don't have to worry about light or them shattering and cutting you. Plus cornies weigh a lot less than a glass carboy and you can shoot them with a little CO2 and push any Oxygen out.
I've got Charlie's book and I like it. IMHO John Palmer's "How to Brew" is a little more up to date. Palmer also has a web site
www.howtobrew.com