H1 transfer after approval receipt before start date and in OPT

[dexterslabaratory]

Already have H1B approval(Masters Category)-. Since my OPT ends 2-3 months before October i will be in CAP GAP, but planning to take a STEM OPT instead. Company A visa was approved and I will get H1 approval notice. Now I want to move to company B who are still not E-Verified. What are my options? Need to send B with clarification, pros and cons info.
1) Ask B to be E-Verified Move to B on STEM Apply transfer of H1b. B wants to know how much will it cost and procedure and if it will need A's permission.
2) Be in CAP GAP - then transfer.
3) if 2 fails apply STEP ask B to be E-verified
4) if 1,2,3 -transfer fails ask B to E-verif, apply for H1 next year.
5) B wants atleast 3 yrs of my work
B needs info on procedures, cost etc before proceed to nxt interview. B is very small compny than A.

[kabkaba]

Note the following things,
If H1 is approved with change of status, your F1 status and OPT ends irrespective of whether you have applied for OPT Extension or not. You must join A from Oct 1, unless B has filed their H1 petition.
STEM extension can be filed before current OPT expires.
You can only work a EVerify employer during OPT extension but any employer during cap-gap.

Here's what you should do if you want to join B.
Ask them to file H1 petition for you with change of status. It will be cap-exempt.
Join B at any time. If you want to play the safest join them after their petition gets approved.