4ft tank sounds like a good size to work with but you still need to find out the gallons. A thread on exactly the same topic as this was done yesterday, if you check out the link it may give you some ideas on which livebearers you prefer;
http
/www.fishforums.net/index.php?showtopic=120519
Gouramis are quite a specialised species, checking out the pinned articles in the Gourami/Anabantoids section will give you alot of insight into which are the peaceful species and which are the agressive/semi agressive one and what size tanks they require.
Most people will have some bottom dwelling fish, like a group of corys or a type of plec, a shoaling species like tetras, barbs or danios and a centre peice or mid to top dwelling species. What sort/types of fish are you into other than livebearers

? Bettas are ok, but male ones don't make good community fish and females require to be in large groups of at least 5-6 to spread out the agression between them.