Your thread topic and poll topic seem unrelated, as does most of the content of your post.
I will try and hit all three items.
Building the Guillow Dauntless kit is certainly within the capabilities of someone 13 years old.
Successfully building an R/C conversion of the Guillow Dauntless with sliding cockpit and operational retracts that flies stable at less than warp speed will depend greatly on your previous building experience, how much time, research, and possibly money you are willing to put into it.
Here is a link to a thread on rcgroups.com that has much information about Guillow conversions in general and includes some info on the Dauntless in specific.
http://www.rcgroups.com/forums/showthread.php?t=278820
The choice of brushed or brushless power frequently comes down to cost but some r/c conversions of static models almost demand the size and efficiency (to enable the use of smaller battery packs) of brushless motors. I would suggest that this build, as your goal is to include retracts and I am guessing at least two control surfaces would be a good candidate for brushless power, LiPo battery packs, and as small (lightweight) of servos and receivers as you can get away with. Use only as much glue as is needed, go with one of the very light covering options (poly span, so-lite, doculam, etc), and you may certainly wind up with a nice, flyable, conversion that includes retracts.