That depends on the final delivery.
YouTube needs other requirements than your charity project I guess or a DVD.
AVCHD footage is in HD and your camera records with a video resolution of 1920 x 1080 pixel, but the specs on Sony's product page for your camera don't state if it is interlaced (1080i) or progressive (1080p).
A DVD is not in HD but in SD (Standard Definition) which has different maximum resolutions depending on your use of NTSC (the broadcast system used in the USA and Japan and some other countries) or PAL (the rest of the world with some exceptions).
NTSC offers a maximum resolution of 720 x 480 pixel, PAL offers 720 x 576 (sometimes it is displayed in 1024 x 576 with 16:9 footage).
YouTube also offers different resolutions, but YouTube makes its own conversions so if you give them the maximum resolution you can get, they will do the rest.
You also need to consider codecs.
AVCHD footage uses the H264 codec, an MPEG-4 variant, as does YouTube. Video DVDs use the MPEG-2 codec.
Both those codec use so-called Group Of Pictures (GOP), meaning not every captured frame is saved, but every 15th (MPEG-2) for example, thus the between frames are only calculated from the change between the two stored frames.
Those GOPs are not ideal for editing, as editing applications need every frame to make exact cuts or other kinds of transitions.
Thus FCE (and other editing applications) convert the highly compressed (and lossy) footage to a codec which offers every frame to be used. FCE uses the Apple Intermediate Codec (AIC) for example, which takes up 40GB/hour if I remember correctly.
In order to use the final sequence in iDVD just export the sequence as a .mov file (.mov is a container for a variety of codecs) with AIC and import that file into iDVD.
iDVD should in most cases take care of the rest, the proper conversion for example.
For YouTube it is better to export the final sequence as a .mov or .mp4 file usinf the H264 codec, which will save space and get you shorter upload times, as YouTube has a file size limit of 1GB if I remember right.
You can also export from FCE like you would when you export for a DVD and then use MPEG Streamclip (
www.squared5.com) to convert that AIC encoded .mov to a H264 encoded .mov or .mp4 file. MPEG Streamclip gives your more options on bit rate (therefore maximum file size), video resolution, audio codec (aac or mp3 or something else), aspect ratio and so on, if you feel up to it.
I don't know what your final product for your charity project shall be, a DVD I suppose, but you can ask for more information if you feel the need.
What do you mean by memory drive?
PS: That is a lot of information I might have given you and I hope it does not overwhelm you, but if it does, don't be afraid to ask.
But since your question comes up every once in a while, you can use MRoogle (my signature) to search for more information.
Have a good day or night.