HI,
1. Are there any complications of having TPS while GC processing through the employer?
NO. TPS dos not affect any previous status. Your H1B status will not be changed. If you PERM is approved and I140 approved (do Premium processing for 15 days decision), then you can extend H1B for another 1 year. find how you can extend H1B for another 1 year, there is a room for you.
2. Can i just file TPS for now and Apply EAD later after 4 months?
Its better to file TPS with EAD. You have H1B for 5 months, after that use EAD you got through TPS. It takes 90 days to approve TPS and EAD. So, calculate the best time so that you have EAD through TPS if H1B expire.
3. Which one might be good option; Extending H1B or filling TPS ?
BOTH. Since TPS application deadline is coming soon, do not waste time.