I would wait 3 weeks until you add the T3. How long do you plan on running the GH? Are you using it with AAS? please tell us your complete regimin.
Metformin increases muscle insulin sensitiviy. I would still use it even if running IGF-1.
If you are gonna run AAS which you should for the BEST synergy effect.
Run High Androgens, an oral kickstart (releases IGF), and an anti catabolic.
Save the IGF-1 protocol for your Post AAS use. And I would continue GH every day throughout at 1 IUs taken three times daily if possible (3IU total ED) Other wise do the 1.5IUs twice daily. There is no need to do 5 on 2 off. even though alot of people do it that way.
By waiting 3 weeks for the T3 you ensure your AAS are kicking in so muscle wasting will not occur.
The synergy of AAS, T3, GH, and increased insulin sensitivity will produce TONS of IGF-1 so there is no need at this point to supplement any. Especially if running 6 weeks kick start of a High Androgen oral (IE DBol, Drol).
Sure you might be saying OMG thats alot but if your gonna put the money in for GH, T3, metformin you might as well get the best results possible.
BTW have you read Building the Perfect Beast? I would 110% recommend you read that book before using IGF-1, its the only book that explains hormone synergy. Also if you use the Phase Cycles he explains you can stay anabolic non stop by switching periods of AAS and Slin/GH