Welcome!
You have made the right first step... asking for help! We encourage people to take their time to decide which costume is the right one for you. Every costume has it's pluses and minuses. The following link lists all 400+ costumes which have been researched and detailed with descriptions of each part...but more importantly, there is a Detachment link for each group. For instance, if you wanted to build a TIE Pilot, you should go to the Detachment web page https://www.jrs501st.com/ which is where everyone around the world who is trying to build a TIE Pilot should go to find all of the right pieces.
In addition, we have monthly "Armor Parties" which are a great opportunity for new or prospective members to meet the local troopers and ask them why they picked their costume.
So ask away!
How did you learn about the 501st Legion?