A: Texas Secretary of State has a ton of helpful resources, including what documents to be filed, what taxes to be paid, and others. With regards to applicable law or which regulators your business will be subject to, you may want to discuss the nature of your business with your preferred counsel. You should also look into the duties/responsibilities of owning or holding a certain position in your company. There are also post-obligations or tasks that the company has to undertake after being registered, like adopting your Bylaws and naming your officers/directors/c-level executives.
A: Separation agreement is usually helpful when separating with an employee amicably and includes other terms that you want to ask of the other party and which you will also make promises. In other words, it is a two-way (or mutual) agreement. A termination letter is most likely a one-way communication, a notice that such employee is being terminated. You should talk to your preferred counsel to discuss facts in detail and make a determination which one will be the right approach.