5 questions coming from a beginner

[LifeOfAquatics]

1. Do I need a protein skimmer for a 20 Gallon long tank? I’ve seen many mixed opinions
2. Is a HOB filter ok for a reef tank? I originally thought so and bought one rated for a maximum of a 33 gallon tank but very recently I saw a few people say there are like detritus factories and stuff. I really don’t want to buy a protein skimmer especially if I go with such a small tank like say a 20-29 gallon. Would the HOB work fine with live rock and live sand? I also plan on replacing the pads once a month or so. 
3. Should I get a 20 long or a 29 gallon? I originally wanted to get a 75 gallon but chose to instead go much smaller and get some other stuff I want with the leftover money. But a 29 won’t cost too much more than a 20 long right? The sand needed would roughly be the same, just the live rock is the only difference. But a lot of people have said that 29s are awkward in shape and are odd to aquascape, 20 long would be nice cause I would have more light options since the tank is shallow, PAR would be greater. What would you suggest? 
4. Tying in with my previous question, should I get a 20 long, 29, or a 40 breeder? I want to save money and dont feel like buying a protein skimmer. I really want to buy some other stuff as well, what do you suggest? 
5. so in my HOB it has a blue pad with carbon in it, how often should I change this out? Once a month? Week? And instead of buying new pads, can I just use big 6 foot pads that I can cut into the shapes I need for my tank (there are like pond filter pads, the big blue ones I forgot what they were called)? Basically, the mechanical filtration is the one that needs replacing every week/month right? 

[seabass]

1. You don't "need" a protein skimmer in any tank.  People assume that you need them for larger tanks, due to the owners typically doing smaller percentage water changes; but that's not entirely true either.  However, personally, I prefer running a protein skimmer on anything that's not a true pico tank.
2. A HOB filter is very appropriate for your tank, and they aren't detritus factories or even nitrate factories (you just need to keep the filter media clean).  And many nano reefers don't run a protein skimmer on this size tank either.  For media, you can use the media that is made for your filter, or use your own media, in a media bag.  However, I usually suggest not running any biological filter, as your live rock typically performs this role.  In addition, I typically recommend cleaning the mechanical filter at least every week, and changing the activated carbon closer to twice a month.
3. If you originally wanted a 75, and are now settling for a 20 or 29, then I'd suggest going with a 40 breeder.  Your HOB filter would still be fine for a 40 gallon tank.  But as for a 20 versus 29, I'd aquascape them exactly the same; however, the 29 would just have more vertical height.
4. If you are strapped for cash, you might wish to save up a bit.  This hobby can be quite expensive, even for us budget reefers.  Lighting will obviously cost more for the 40 breeder, but the aquascaping and livestock options are worth it, IMO.
5. You can certainly use your own pads, and even put activated carbon in a media bag.  See above about cleaning and changing the media.

[seabass]

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