Honestly, I don't know when the TYBW manga starts. But you could search manga databases or ask in manga enthusiast communities to get the details you need.
Their relationship would likely become more intimate in a different way. There would be a deeper level of trust and reliance. Ichigo would see Orihime in a new light, as the mother of his child.
I'm not sure about a specific 'Ichigo and Orihime lemon fanfiction' title off - hand. But you can often find great ones on fanfiction websites. Just search for 'Ichigo Orihime relationship fanfiction' and look through the results. You might have to sift through a bit to find the ones that are well - written and suit your taste.
The TYBW arc's starting chapter isn't a straightforward answer. It could be different based on the manga version and region. I suggest looking at dedicated manga websites or asking fellow manga enthusiasts for the exact chapter.
I'd suggest checking manga forums or dedicated Bleach fan sites. They often have detailed breakdowns and recommendations on where to pick up after a specific part. Sometimes, the author or official sources might provide cues as well.