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You will need to get a Airplane instrument rating too before your CFII, likely more time for a Commercial requirements, a new long crosscounty in a airplane.  Read Parts 61.123 and 61.129 very carefully for the most part that spells it out for the Commercial, for the instrument extra requirement are spelled out in the lengthy Part 61.65   You may well be able to combine the rides, but the DPE will charge for two.

You then need CFI and CFII training and another double fee combined checkride.  Read Subpart H, it starts at 61.181

All are doable, just a little more involved than you thought, but not too much.  You did not say where you lived so I can't say anything about training.