Structure Engineer, foundation repair in south of Dallas, TX

[Selina Gruden]

HI BP Family,

I am new to TX area, recently purchased a property in the south of Dallas, TX, and the property needs foundation work and some repair. It is my first time to deal with foundation issue. And I have searched in BP forum, couldn't find the answer. So I would like to post here, hope someone can share the light with me. Thanks! Here are my questions:
Do I need to hire structure engineer to get the assessment and recommendation what need to be done, or should I directly go to the foundation repair company?  Is repair company has enough knowledge to solve the problem, or it is worth to pay for the structure engineer to make sure the work will be done right .( I got quote from Cross Town Engineer for $720). Do all repair work needs to sign by the engineer after? Do I need to file permit or paper work to the city etc? Can anyone refer a good, reliable foundation repair company and structure engineer to work with?And how many years warranty do they offer most time?
Thank you!