When I am in my OPT I did apply for TPS EAD. I used my OPT first then TPS EAD. I am glad I applied for TPS EAD So I can keep my job because If I applied TPS EAD later on who knows how long it will take.
I dont think your OPT will get denied . Yes you can always apply TPS EAD later though I am not sure how long it will take USCIS process your EAD.
And also TPS EAD you can apply directly for GC if your employer is willing to sponsor.
From OPT EAD you have to go through H1 lottery system
Pls check previous thread related TPS to GC
Good Luck