Clarke has only 1 album with Mode(1st album)(above hits that I said are from post Clarke area),which is more anolog+sampler mixture.
yes you can buy cards(SM,compact flash)-they are same as Digi cameras.
No PC speakers(mid range lack) are'nt good enough for workstation monitoring-go buy active or passive studio monitors or high end KB amp or PA.your home stereo system(good one)(with AUX in) can do it for now.
make sure you listen to big three(korg,yam rol)cause you can sell them easier and they have numerious 3rd party support(sounds,styles,forums).
dont forget you can't have it all.some are better in some areas but not that good in other area.You MUST listen to them.onboard sampling is a must for own synth music.
on onboard(and expendable) sample mem-roland fantom S and X has the largest of big three.(but they lack real time record-with seq-you have to retrigger them).(both yam and korg do that).it has pads which are a major help for both sequencing and live.
motif has good acoustic sounds,breath controller iput(great for reed-remember those DX7's sax and brass),M-lan,but OS can be painful.
triton on the otherhand is the easiest to use and the best seller(no presets occupying ROm-all patches and performances can be all rewritable-another major selling point for Korg worstations,but ac piano and some acoustic sounds are weak.but onboard sampling can help.again user sample max mem is still less than roland or yam.
but the sounds-you have to listen them.all of them can do decent production in the right hands.