lol well your doing a few things wrong
if you just want to check a walkthru or look for some hints this page :
http://www.classicgaming.com/starcontrol/ has probably all the info you need but ill answer what u asked in ur post anyways
the umgah caster is in the possession of the spathy basicly just allow your alliance with them to run its course (u are allies by now right?) and they will one day give it to u out of the blue there is also another caster in the game that does the exact same thing, im forget where if u wanna know look on that site i mentions for the burvux caster (or a name similar to that)
there are several rainbow worlds rather than list them here go to the site
when u give most of the locatoin to the melorme u should have alot left over, with that u can buy fuel from them and save urself some creds
no u cant build mines if u look on that site u can find a list somewhere of relly rich mineral systems mabye u should try that but yeah i always found mining a pain in the ass. if u sell one of your casters to the drugge they will fill your fuel tanks to maximum capacity no questions asked, so heres a way to stick it to them outfit your starcrusier with nothing but the advanced high capacity fuel cells ie get rid of ur guns and crew pod and anything else and just have fule tanks then sell a caster then got back to sol and sell all ur fule, that should be enuf money for quite some time
also hyperspace is not a good way to travel, look on that site for how to get the 'quasi space portal spawner' that will save u alot of time and money, its to long to explain how to do it and this poist is alredy a mile long
hope that helps