A "tile guide" can be a good idea for the novice as it is a tile replacement, but nothing beats well cut tiles made with a diamond head on a rotozip. Even if the tile rounding is a sloppy job, that's fine as long as the toilet covers it asthetically. Correctly installed tiles on good thin-set will be hard enough to resist cracking from even the tightest toilet to flang bolts.
There are reasons you want the flange to be as close as possible to the toilet, less wax is better. I've seen too many DIY'ers have stacked as many as 3 wax rings, and the problem with that isn't the wax, the problem is that we don't have x-ray vision to see how well aligned it is. A single regular height wax ring is more forgiving on toilet alignment errors, mostly because the toilet is right over the flange and gravity does all the work without pressure. Only enough wax is needed as a gasket to protect whatever wood is nearby and prevent sewage gasses from coming out.
Obviously if the flange can be replaced with one of many aftermarket goodies from Oatey, Sioux Chief, Danco, etc., then please do it. Get those new tiles under the flange, and holes only need to be approximate to clamp that flange down to the floor screws. All the stress of the toilet is going to be fastened to the flange, from people sitting on the toilet, leaning on it lopsided, hugging it from a hangover, whatever external brute force applied to the toilet.
On situations where the flange can't be replaced, because it all seems to be part of the concrete, or an old-school cast iron flange (a pipe that's been hammered out to flare), then you'll need more trick items, specialty taller wax rings, or one of the many waxless rings.
But why is the floor height being increased in the first place? Some DIYs will tile over tile, or tile over hardwood floor. Do a better job by cutting out the floor, make a new subfloor with a layer or two of plywood, Schluter Ditra for those that must, and you'll be restoring the floor height as you tile it. I don't like doing stuff twice, I want to know that subfloor will be so solid that I can jump on it afterwards and no tiles nor epoxy grout will crack.