I want to replace my current old water heater with tankless but I am not sure which is the best and what capacity I would need? I need your expertise before I make a decision.

1. 1500 sqf house - 2 baths - 3 people.
2. Which model you would recommend and BTUs?Noritz, Rinnai, Tagagi?
3. Our current water heater is in the middle of the house where the bathrooms are - actually very close. We like to free the space for storage. We are in CA and we can put the new unit outside but the problem is that if we want the unit to be close to the baths and kitchen - then it should be installed outside facing the back yard. The gas meter is far away on the side of the house and if we install there I am afraid we'll be waiting for the hot water forever - it will be close to the gas line but away from bathrooms and kitchens. I am stuck - I don't want to see the unit in front of me every time I am sitting in my back yard. What is the best reasonable distance to the baths and kitchen? I know closer is better. I also have 13 windows so by code it cannot be close to a window - I have a maybe 2 options - facing the back yard on the wall in the middle of the house or on the side close to the gas meter.
4. Are there any options to put it in the attic ( or crawl space ) or it's more expensive - venting etc.
5. We are also buying a new furnace and moving it to the attic.Do both units share a gas line ( pipe ) or they need to have two different pipes?
7. If my furnace is 80-90,000 BTU - what size of pipe I would need for both if sharing?
8. Does my gas meter needs to be upgraded? The house is 1953.

Sorry for so many questions - thank you in advance!