The internal memory of 8GB is not fully user available because Android OS and files take up about half of it. So availability for user is near about 4GB. You can root and remove bloatware to increase internal memory if you want. Alternatively you can swap int/ext memory. Changing file systems and partition size is beyond the scope of this discussion
A part of the 1GB RAM is required to run the Android OS in itself so you will never get fully free 1GB RAM. Again, removing unnecessary apps, especially apps which start on boot, can increase RAM. And RAM has nothing to do with SDcard / external storage capacity unless it is required to initialize and run the card itself
"From the legacy of GT-I5801 to I9082"