Make Oracle SQL Developer act like PL/SQL Developer
The preferences dictate when the code assist features kick in. In 4.0.3 we filter the advice for the automatic bits when there are more than 10 suggested identifiers. So, typing:

select * from 


...on a large schema, you'd likely not see any suggested table or views names, unless you invoked the helper directly via ctrl+spacebar.

As you type more, the more likely the suggested values will be of more value. The default settings will have automatic popups after .6 seconds and the number of hits goes below 10.

Tools &gt; Preferences &gt; Code Editor &gt; Completion Insight


Make sure you don't have the first two items disabled. And try increasing the filter to something higher than 10. Examples of different insight 'helpers' and a video demo here. 

You can set your own NULL text, that's in the preferences. I have a bug logged so you can set the NULL coloring AND use the zebra styling (fixed in version 4.1, soon to be released.) And I also have an ER logged for custom colors on the 'zebra' styling.

We fixed that bug, go get v4.1.1 - null color + zebra grids work now.