I recommend Optima red top for starting. My Optima lasted 10 seasons before replacement with, you guessed it, another Optima!

As for connecting directly to starter, that is an option. I would use an On/Off Battery switch to isolate the starting battery from use after engine is started, tho many would suggest use of a combiner. Strictly personal preference here.

For house batteries I highly recommend two Trojan T-105 225 amp golf cart batteries in series to produce 12 volts.

Also, a good battery monitor will help get longest life from batteries.

BTW, you can buy the red top online delivered at a low cost compared to the local auto stores.