A lot of folks have ordered their wires, very competitively priced, from GenuineDealz.com where despite the kitchy name, they have premium marine cable AND they will put the lugs on for you at about the same price you would pay for just buying lugs. No need to buy the expensive crimping tool that way, very much worth looking at.
Mike at Genuinedealz is excellent.
Unless I misunderstand how an echocharger is supposed to be installed, I think you have the "on/off" and '1/2' switches and echocharger miswired. You don't need the on/off switch. If you select #1(a) from the a/b/both switch, you connect directly to the starting battery. If you select #2(b) you get the house battery. And then you let the echocharger connect from battery #1, your starter, to #2, so that whenever you have started and run from the starting battery, as soon as it is topped up, the echocharger starts charging your house bank as well. (Or vice versa.)
If you start from "all", the echo charger becomes a moot point since you're then charging all. BlueSeas and West should both have topical diagrams on their FAQ/advisor pages.
I suspect he is trying to add a dedicated start battery but also retain all the redundancy the 1/2/BOTH has.
I thinks this is what he was aiming for.
With this simple but very redundant system you retain all the isolation & redundancy of the 1/BOTH/2/OFF switch, already there on most boats, yet add a dedicated direct wired starting battery. Simply flip to #1/HOUSE and ON and your ready to go. When you're done flip both switches to OFF.
If the start battery were to fail flip the ON/OFF to OFF and the 1/BOTH/2/OFF to BOTH and now the house bank is starting and providing house loads. Conversely you can still use the start bank to power house loads in an emergency with the 1/BOTH/2/OFF in position #2 and the start switch to ON all while isolating the house bank in the event of a failure.
This system is more complicated but ultimately considerably more flexible than some other systems where you must use the "combine" feature in an emergency. Three properly wired ON/OFF's will do the same but now you need three switches..
I'd also suggest looking for battery switch that had "field disconnect" terminals built into it. With most alternators, if you switch the batteries while the engine is running, you can blow out the alternator. With a switch that has the extra field disconect leads, you can't do that.
Not necessary with his diagram as the alt will always see a load. The alt is fed directly to the house bank and the Echo takes off of there.
Some, not many but some, alternators have internal protection which makes this a useless expense. But as long as you are starting from scratch, take a look into it.
I think some of the newer Valeo's on Volvo's may have avalanche diodes but his factory Motorola would not. Beyond that I know of no "marine" alternators that use avalanche diodes, as of yet..
My only "critique" would be.
1- Consider fusing the start battery. 1GA wire with a 105C jacket can handle 245A outside an engine space and 208 inside. However for short circuit protection the ABYC allows you to go to 150% of the 100% ampacity rating. I would suggest a minimum of a 200A ANL or MRBF fuse if you are starting the engine...
2- The house MAY need to be used for starting loads, it is wired so it could be, so that fuse and all wiring to and from the house bank should be the same gauge as the starting circuit both - & +... 6GA is quite small for starting a motor. Unless your house bank can never be used for starting purposes, meaning no "combine" switch and no electrical way to do it then the house bank wiring should be sized for starting loads.