Hey Suresh - duplicating my answer here on YT - I would agree that hand prepping is risky unless you are REALLY good at it, which I'm not. It would be too easy to get a dip or round off the edge I think. I've seen it done (I think there was a video by Joey/King of DIY), but I personally wouldn't try it, especially with thicker more expensive material. You could try either a woodworker shop (who might not want to work on acrylic, not sure), or try a sign shop to cut your panels on their CNC. That might eat into your budget, as I imagine having them cut the panels would add significantly to cost. BTW, I'm only using 3/8" acrylic (10mm) on my sumps, one of which is about the same dimensions as yours (even longer), so using 18mm seem like overkill unless you are not adding a top rim or any bracing to help the long span not bow. I'm all for over-building though, so thicker acrylic is better in general : ) if not cost-prohibitive. Sorry I can't be more help on the edge prep, which is even more difficult the thicker the panels - as it gets more difficult to keep the edges perfectly flat and perpendicular to the sides the thicker the panels. If you do end up having to hand prep, you might buy some material and practice before trying it on the real sheets for the aquarium. If you were in my area I'd invite you over and do the edge prep for ya!