My quick googlefu says Texas's franchise tax (business margin tax) doesn't apply under $1m, so you should be ok sitting on the LLC (you're lucky, here in Caly we don't have it so easy). But I don't do business in Texas, so take it with a bucket of salt.
For your fed questions -
yes and yes
not sure what you're referring to?
I'm 99.99% sure there's no excise taxes on electrical panels, but what do I know
I would highly rec talking to a tax attorney or enrolled agent (EA would be cheaper) who has experience setting up new businesses for people, if you got the cash to spare (business deduction! haha). I understand the desire to want to do it all yourself, but having someone to hold your hand in setting up an LLC and the rest is a huge help, and they should be able to answer any damn question you have (quarterly taxes, potential strategic purchases of equipment for non-depreciating purposes, explain the common fallacy of write-offs/business deductions, noob mistakes not to make to keep your LLC a legally defensible LLC, insurance(s) you should carry, etc etc), other than your industry specific stuff. You'll also want help (at a minimum) on your first year's taxes too so it's good to have the same guy(s) throughout.