The shoots i would imagine will need to be large enough to start growing their own roots, This is the only way removal will be successful. but as the trunk of tree ferns consists basically of the main ferns roots, i think that you may cause more damage to the fern and the young shoots removing them with enough of their own root (probably hard to differenciate from those of the main fern), than its worth.
Not sure why its only producing small fronds and not many.

depends on what is growing from the side of the fern, in my experience the only thing i have found growing from the side of Dicksonian Antartica is Acacia fronds, which (with care) can be grown seperately.
Its still early in the season yet, leave the fronds and see what happens, i have just bought several into my garden centre and they dont have any fronds yet..

Thanks for the replies. I shall leave well alone. It was probably the very hard winter we suffered this year. The ferns growing from the side look exactly like the main fronds, so it may just be possible to break off the growth and start something new, the base does seem to have a bulk to it, but I will leave it for the time being. Thanks for the advice, only just joined here so will be a regular now!