I have a 2016 Anthem 44b with eight ( Relion 6v AGM House Batteries that need to be replaced and have a few questions before investing:

1. Is the higher the AH (amp hours) the better?  When I'm 90% hooked up to shore power, allowing the Inverters to charge the batteries whenever necessary and as often as necessary?
1: As long as they physically fit.
2. Can I remove ALL house batteries at one time (at least 24 hours) to clean tray and install new batteries, without having any problems, once power is restored?  As long as solar panel is covered from sunlight, inverters are turned off, generator is off, and unplugged from shore power?
2: don't need to cover solar panels, just make sure all positive cable end are insulated. Piece of garden hose works great.
3. Is ordering batteries online worth it?  Mainly due to the heavy Weight and the hazardous material?
3: Don't know if they still do but Battery Guys Battery Guys - Nationwide Battery Distribution | Battery Guys offered free shipping when I got mine a year and a half ago.
Also, take pictures of the wiring before unhooking, label all wires. And contrary to normal thinking, disconnect positive cable first, per Magnum inverter/charger manual.