Making a bootable usb is absurdly easy.
How/Why does cat write a bootable ISO to a device
Assuming here that the usb is /dev/sdb
cat file.iso > /dev/sdb
I don't understand why you don't just clone the first disk you installed to then tweak the few things you need to change, like /etc/hostname, maybe nic ids, there's not a lot that requires customization.
Wnen I used to do a lot of distro support, one of the most frequent problems we encountered was people burning the install cd/dvd using too high a speed, which led to corruptions in the optical disk data, which led to strange failures. Also, of course, low quality optical disks cause issues as well. Audio and Video optical disks support a significant amount of data corruption for playback, which is why they still work when scratched etc, but that type of corruption makes binary data like you'd find on an install iso totally fail, or fail in odd unpredictable ways.
USB is obviously the preferred method because you don't have those types of issues in general, plus you don't have to keep making disks that you are going to throw away, but not all machines boot from usb.
[added in response to comment]
First, when you 'copy' data, that's not the same as writing it with cat to the usb device. cp vs cat > that is, though cat or dd do copy the data directly without any changes to the usb device, while cp would copy the data to a partition made on the device, which would not be bootable of course. So that wasn't clear. If you used cat as I indicated, then you have another issue, possibly a bad usb drive, possibly the machine does not support boot from usb, possibly you didn't trigger the boot menu option to boot from the usb device.
However, because cat is so easy and simple to remember, there's no reason to complicate the matter further. Note that the iso contains the bootloader. The link I posted has some good explanations of this process so I won't repeat them here. But if you cat the iso to the usb correctly, and if it does not boot, you have another, unrelated issue. For example, several of my systems don't support booting from usb, they are older.
Second, no, I wouldn't clone a disk from a running os, from itself, that is, that's because the running os has a lot of stuff happening live which I don't want to copy to a clone, logs, all kinds of stuff, you clone it once you've gotten the install on it exactly the way you want all the machines to be. Since you have > 1 machines, that's easy, just boot from a live system maintenance cd, and do the cloning from there, that way you know that the cloned disk is going to be the same as the resulting disk. ultimate boot cd has a lot of options like that, parted magic for example give you a good working environment.
There's an alternate way to do it, which is to clone just the partition the root drive is on. That's what I would lean towards doing because it avoids potential issues with cloning different sized disks, but then you have to manually install grub onto the system, a true disk clone clones the boot sector as well. I'm not sure about clonezilla for example, ideally you can clone just the partition and boot sector, some cloning tools support that option, others don't.
Note that you can also simply connect the two disks (to be cloned, and clone) to a different running system if you have external usb drive devices, then clone them that way, that's easy.
[update 2, in response] Note that if you get a specific error message, just google it, and you'll find the answer, which is probably maybe this:
I came across this problem(
isolinux.bin missing or corrupt) recently.
The flash disk is made by dd, the iso file is of 12.04.3 64 bit. I fix
this by change BIOS setting: change
USB Flash Drive Emulation Type
from 'auto' to 'hard drive'. Hope this helps.
It's also possible your downloaded iso is corrupted, which you can verify by checking it's md5 sum.
note that you don't need to pay attention to the dd stuff in that thread, cat is easier. I assume you did the cat as root?