Oh yeah see if you can grab a 40 breeder during those 1 per gallon sales. They make great sumps
Mags like everyone said you will be fine with a 120 for a very long time if not the life of the fish.
I would still definitely go with a sump. The pump can be used in your 180 if and when you decide to upgrade. Trust me sumps arent that hard. Once you get one done you're going to be amazed at how easy they are.
As far as used tanks.... well it depends how your area is. I could never fine a decent sized tank that wasnt much cheaper than buying new. Plus for peace of mind it just wasnt cost effective. That being said i would still explore used tanks. Take pics and post in the filtration section.
Another thing is having the tank drilled. I would definitely go that route over the diy over flows or the hang in back over flows. I had one on my 150 and it flooded my garage. So to sum it up i would probably spend the money on a new tank and have it drilled.
Do you have access to a variety of LFS ?
Oh yeah see if you can grab a 40 breeder during those 1 per gallon sales. They make great sumps
very rare for used acrylics to leak when compared to the amount of used glass tanks of the same size. If you can't wait get the 120. It can always be used as a chamberless sump for a 180g+ down the line.
So i definitely agree with rocksor. A used a acrylic imo would be a better choice, easier for you to post pics and have the seems inspected by other members.
So when i mean drilled om talking about the holes in the tank that the plumbing (pvc) would run through. With an acrylic tank its easy peasy. We can give you the dimensions of the hole when the time comes. With glass its a little trickier. Other members do it with there eyes closed so even then its doable just need the right tools to cut the glass. Biggest issue is most tanks are tempered glass which cannot be cut. On the flip side most tanks bottom panel is plate which CAN be cut.Fish Tank Travis uses a laptop to tell the difference so keep that in mind when you go tanks shopping. Out of curiosity what would your lfs want for a new 120 with 1 over flow 3 holes drilled ? Also get a quote for 2 overflows 1st overflow 1 hole drilled 2nd with 2 hiles. Im just curious.
Stop worrying about the sump. You git this.
Another benefit with the sump/overflows besides the maintenance and endless amount of bio media you can fill it with. Is how easy the water changes become. I literally have never vacuumed my substrate in the 300.