I have a J ticket on Turkish Air IST-BKK-USM with a 6 hour layover at BKK on 22 June before flying TG in J to USM. [Departing via Thai airways in F BKK-SYD on 4 August.]

I'd prefer to leave either my carry-on or my larger checked suitcase at one of the BKK left luggage counters (Chubb, etc). Will only need colder weather gear again when I move on to southern hemisphere winter and high elevations.

Will I automatically have to pick up all my luggage and clear customs in BKK and pass the level 4 / departures Chubb counter as part of the natural transit flow? Or do I need to give the airline any special instructions to ensure my checked bags don't end up in USM? If I need to pass through security again, is the J fast-track actually fast? Lastly, will I pass a lounge suitable to rearrange a few items between my bags before doing this?

Thanks in advance.