TLC5955 Combining 48 outputs to 3 | PCB
No.
Regulators need to explicitly designed to allow putting their outputs in parallel, and this is seldom done because the complexity of that is usually not worth it. You can see regulators like this mostly in computer mainboard designs with currents upwards of 100A.
To drive a 1A LED, use a single constant current regulator. The current is too high for linear regulators without elaborate cooling solutions, so a switching regulator is a way better idea here even if it needs a bit of stuff around it. Trace width should not be much of an issue there, but it is a good idea to use zones instead of traces nonetheless.
For manufacturing, use 2 oz copper thickness and either 1.6mm or 1mm PCB thickness. There's nothing wrong with others, but these are standard, so these will be cheap as your design can be combined with others for manufacturing (so the fab house will not make a huge PCB with ten copies of your design, but ten PCBs each containing ten customers' designs).
I've packed up an older project of mine, a four channel 700mA LED driver, feel free to steal parts of the design. There will be a lot of impractical aspects for you like the connector that you need to change, and you might also want to separate the LED supply and the regulator supply (for which I use the same 5V rail). Each of the components I use is in the smallest possible package, so if you don't want to solder 0402, you can use 1206 or larger instead if you rearrange the board a bit, and you definitely need to change the value of the resistor setting the target current.