Have you tried google? it has pretty much of amateur forums and other sites with this kind of information but beware there are a lot of misinformation also , now try a search read some stuff and if you still have questions come here and ask.
No offence but some questions are easy enough that you can find them yourself.
Bifilar is okay just as much as single litz wire is okay because when it comes to high frequency the bifilar coil already is a litz wire so if you have a litz wire with say 5 strands I think it is pretty much okay , for further information you either have to see some sources or conduct experiments and see in real life under what type of wire wound you can get the best field strength and angle.