Yes the Music Hall would be an improvment over the Gemini, although i understand some of the Gemini direct drives were quite good. The main weakness with most DJ decks is that they are based on the Technics SL1200 which, although a very fine deck, has a pretty poor stock tonearm easily bettered by more modern high-rigidity designs. The Music hall is also compromised by it's tonearm so I would look at a Rega Planar 2 or a Goldring GR1.2.
So far as amplifiers go I would tend to go for a dedicated amp like the Cambridge Audio A5 which has an optional phono stage rather than a receiver. If you want a radio there are so many really stunning tuners going begging on ebay for next to nothing which are sure to outclass the Onkyo.
For speakers I would consider something like the Acoustic Research
http://www.amazon.com/gp/product/B00...lance&n=172282
or Wharfdale Diamonds, depending on how small your bedroom is. These kind of speakers and amps are designed for UK sized rooms which average about 15 feet square. This is small by US standards.