Move the starter wire over to SW2, upgrade the wiring on the start battery to 2/0, fuse the solar, alternator, and charger wires, and you're done. The plan would be to leave the battery switch on Bat 1 and start the engine with Bat 2, unless it fails--then you would turn the battery switch to Both.
It is a 1/2/BOTH/OFF.... Most folks with 1/2/BOTH/OFF switches simply leave it on the HOUSE and do everything in that battery position, and keep the #2 as a reserve.
The diagram looks great just add some fuses and you're good to go. My only concern is a 55A alt on AGM's.. I have seen far to many cook themselves when asked to charge large banks of wets and smaller banks of AGM. If you can get an alt shop to convert it to external regulation, and then you add an alt temp sensor, you'll be okay with AGM. Keep in mind that both AGM and Gel cells can still vent if over charged and the ABYC makes not "exceptions" on battery venting requirements of wets, gels or AGM.. If charging wet cells properly this is pretty much a non-issue and the vast majority of boats in the world have wet cells, most of which are in cabin spaces...
As Don said your #2 bank should also be the same battery wire gauge as the other bank. 2/0 is generally a good size...
The ACR should ideally also be fused if those wires could cause an issue. Blue Sea also recommends a 15A fuse in the neg wire of the ACR on top of fusing the pos leads..
Technically you'd be covered by the bank fuses if you changed the ACR wires to 2/0. 2GA can not be protected be a 250A fuse. The max ampacity rating for 2Ga outside an engine space is 210A. You can also go larger on those fuses as 2/0 can be 330A outside an engine space for 105C wire.
Consider that the engine space is a poor location for battery so if you have room somewhere else it may be a good idea a to consider that.. Heat is the enemy of batteries when it comes to longevity....
Your wiring for #2 is 2Ga and that is only rated for 178.5A or a 175A fuse inside an engine space. By going to 2/0 you can keep the 250A fuse as you're protected to 280A inside an engine space with 2/0 wire.