You should be fine with a 4x54 but I would at least go with a 6x54 model and if you go with a 8x54 model you should be able to keep whatever you want. And one nice thing about the 8x54 model you can always not use as many bulbs and it can grow with you needs.
Just my opinion.
I have a 8x54 on a 72 gallon bowfront. And depending who you talk to I should be unlimited on what I keep. But I haven't tried it yet.