Please help! B1 revisit.. Urgent! "Edited question"

[Sund1]

Hello 

I recently traveled to US on B1 through my company for 5 weeks for trainings and business meets. The stamping on my passport is valid till August end. 

My questions are:

1. Can I re-enter US for the same reason with the previous invite letter?

2. And Do I need an invite letter to re-enter if I travel within the stamping dates (my stamping is valid till Aug 3rd week.)

3. Also, will they stamp a new date on my passport from the date of re-entry to US for another 180 days? Or will the stamping date be same and remain as August last week as it is now?

4. Should I have a return ticket as well? If yes! which month should I book the return ticket to? 180 days from my date of re-entry? or Aug last week which is currently the date on my stamping?

Please let me know if you there is any info required from my end. 

Thanks!