Yes you will need a box to transfer your designs to the machine.
And the larger alphabets can be bought from different designers (just google embroidery designs and you will find plenty) or
you can download them for free on the sewform.
If you need to resize your designs, there are some free programs you can download. One of them is truesizer from Wilcom
http://www.wilcom.com.au/PRODUCTS/TrueSizer.aspx