It looks very "natural." I would suggest a trim and perhaps tightening the plants into specific placements, but that is only a suggestion! Otherwise, your ludwigia cuba is friggin' awesome!
As far as U. Grammifolia, I would suggest that you find someone online (a store) that will ship world-wide. People here in the States have it, but may have trouble sending it to you. I would think that one of the Malaysian online shops might be able to help you, or you could try Aquabid.com.
That's even better if you have a local utricularia!! The use of native species in any aquarium can be a pretty cool thing! I'll be interested to see what it looks like once you've been able to incorporate it into your aquascape.
As far as mixing your plants: It is just what I am used to doing (separating plants into tight bunches). However, alot of "biotope" aquariums incorporate a lot of "mixing" as it makes it look more "natural." As long as YOU like the end result, that's all that matters!!
The local utricularia is as not as beatiful as the graminifolia, but let's see how it develops. I will try to take photographs of the process.
I mix a lot the plants because every time they offer free plants in my argentinian forum ( http://www.croa.com.ar/foro/index.html ) I always accept !!! jejeje. then I don´t know where to put them since I have only one tank !!!