yes, usually one piece of granite runs into another an forms a flushed seam.

It depends on the granite type (different types have different strengths) and the size of the area. Quartz is a stronger product. Try to avoid seams and sunlight.

It depends on how far over the L portion goes and how big the slabs are. If you have a nice breaking point like a sink close to the L, you may be able to seam there and keep it almost invisible. Your granite fabricator should be able to help with that.

Hmmmm...Who told you that? Very odd concern, and doesn't sound like a concern an average homeowner would have. What kind of floor?

It sounds like a two man install 8-)

If a fabricator / installer has concerns about a "L" piece breaking during travel, and/or install ( I'm assuming this particular piece can be fabricated with a single slab ) and instead of making excuses, they should speak up and let the homeowner have the option of getting what they really want

If it is a large piece and does require a third or fourth person for a seamless install, it would be an additional cost, a normal install crew is two.