A 4 foot tank will limit the number of Cichlids you can keep - especially if its only 12" wide... You need to go for as decent a size as will fit your room without taking over and that has a decent overall volume: Length x Width x Height.
Which type of Cichlids do you want to keep, South American / New World, African / Old World? The amount of fish you can keep will depend on this. The biotype will also be different for different cichlid types e.g. plants will be a waste of time in a tank full of Malawis and they need a rocky habitat.
Can you handle owning aggressive fish? Many Cichlids are just that, and you will need to do your research on what you can and can't keep with certain fish. You may have to witness a certain amount of fin nipping / lip lock fights / etc and know when to remove beaten up fish / bullies to keep the death toll down...
They are, however, amazing / interesting / colourful / rewarding fish to keep...
There are plenty of links in the Cichlid sections on this site that will give you a good indication of fish types and requirements & compatability issues etc.
You now have some things to start thinking about, and start looking at some of the 'pinned' posts in the Cichlid sections
I'll take another look at this post and have some more time to add some other info in a couple of days or so, when I am less busy at work...