A few questions about this scenario. Flying ORD-LHR on AA in First as part of AONE5. Going directly to Paris, but later leave out of LHR hence the AONE5 going into LHR to save the segment (and to fly in First). Originally the plan was to take the Eurostar, but LHR-St Pancras looks like a headache with checked bags and no familiarity with the area. I'm seeing really good one-way prices for LHR-CDG on BA. So, I'm thinking I'll have the AONE5 into LHR, then buy a BA one-way LHR-CDG.

Will/can AA check my bags through to CDG? The LHR-CDG is a separate ticket, but if I show it to them that should be okay, right? This means I could stay airside when we arrive at LHR.

If I show my AA First stub at T5 Galleries, can I get lounge access? Will they know or be confused by my outbound ticket in Y? Will they know it's not the same ticket and thus try to refuse entry?

Thanks.