Both are important YES, but when I refer to being out of bubble I do not mean by any radical degrees. I have had a 180 gal tank that leaned a little forward for many years and never had any stress issues or leaks. And that tank is still in use today, just not by me. No floor is level and when you start dealing with larger tanks you are putting a lot of weight on the floor. When you start to shim the bottom of astand you are now transfering all that weight onto a very small area of your floor (because now your full stand is not touching the floor). With the 180 gal tank that was almost 1500# of weight and I was not going to put some shims under the stand and cnage the footprint of the stand. Stands are made to distribute the weight evenly on your floor and most floors, unless on a slab of concrete, are plywood and 2"x12". You want as much of your stand to be on the floor so as to spread the weight over your floor joists and plywood flooring.
True but it also depends on the style of stand. The last stand I had for my 60 gallon tank was a rod iron stand. I thought it would not hold, but did the job. But I got rid of that stand and just mounted the tank on the wall, much cleaner and stronger, and the best part of it is I could level the stand in all directions and I did not have to worry about dealing with the floor
No I did not trust brackets. My tank spans 4' and I was able to attach to three studs inthe walls. I opened up the sheetrock and bolted a 2x4 to the wall at a 90*, then for the bottom brace I bolted another 2x4 at 45*'s. The 2x4's tie together near the front of the stand with a home made tounge and grouve. Each bracket (and there are 3 of them) will hold over 400# (or about there, 2 people stood on it). The three braces were boxed in with a single 2x4 as the front face, and the sides were faced out with 2x4, and the backes were all tied together with 2x4's. It took a total of three 8' 2x4's and 12 bolts for a total cost of under $20. The top was covered with a piece of ply wood and everything was stained. I wired a plug just under the stand and mounted a couple of power stips and my light balast under the tank. I ran my hoses for the canister filter through the wall and made a compartment for the filter under the house. It is not bad for a couple of hours of work. I will have to take a pic of it and try to post it, But I miss my big tank, but I just do not have the room anymore