I tried that (macro in the main) despite all the advice I encountered and quickly came to regret it. The stuff is a maintenance nightmare and quickly began to crowd out stuff I paid good money for.
As of late, I have resigned myself to having a perpetual caulerpa problem in my tank. But I did come to one realization: most of my frustration stems from maintenance. Specifically, the continuous trimming to keep it shaped like a little shrub and not creeping around. Now that it's in pretty much every nook and cranny, I do this: When it's time to clean the caulerpa (every month or so) I prune the hell out of it. Just like you're trying to eradicate it. But you won't. There will be some left, some that grows. And I accept that because for most of the time, you can only see little cute bits of grape macro popping up.
So rather than thinking of it as a stable "bush" of algae and trying to freeze it in place, I think of it as type of plant you can harvest almost 100% of and it will "spring eternal" ...
...
Filter:
Again, I really suggest keeping macro out of the display area.
But ... if you just want a cheap HOB get a whisper1 or something and turn the flow down. Take out the filter media and put in a polyfilter pad and a bag of chemi pure. Don't change them when the boxes recomment, that's too often. But keep an eye to see when they get crudified by junk and stuff, restricting water flow. Then change the polyfitler first and a week later the chemi pure bag. chemipure and other similar bags of carbon rocks that soak up pollutants make good surfaces for bacteria after they mature, but do tend to accumulate an unhealthy amount of gunk.
Or, fill the HOB filter completely full of rubble rock, that would make a good filter as well.