You can remove the 3 light bar between the tail lights.
Maybe, maybe not. I think the need for those is determined by load width. At any rate, If memory serve me, if the width of your rig, boat and trailer is 80" then the three light bar is required. There may also be regulations on having certain side lights for specific configurations. I would go to TDOT website nd look up the light requirements. At any rate, I would be sure before removing anything. The regs are easy to find and you never know when you might pass some trooper with too much time on his hands.
Here is a PDF that gives all of the light requirments for the different size/configurations.
Your trailer was probably built by a manufacturer to cover the laws of any state it may be used in, but even if you are not required to have something that is on your trailer, no one ever got hit because they were too visible. Do whatever it takes to restore it to factory condition and go cheap on something else.https://www.txdps.state.tx.us/internetforms/Forms/CVE-38.pdf
The PDF doesn't refer to it, but I did find a couple of sources that say a trailer over 80" wide must have the three ID lights on the rear. That's only 6.5' and I think you would be hard put to find a boat trailer less than that, so I would put the lights on, again, like the trailer came from the factory.