Hi Craig,
Welcome to the wonderful world of yak fishing - you won't be disappointed.
I've always had a soft spot for the Torque - liked the idea of the leccy motor.
PFD. I use the manual inflation yoke type, of which there are many brands out there. You can buy these for around $70 at BCF etc. I like them because they are light and aren't bulky. Some of the old style vests have bulky backs on them and don't work with the high kayak seat. But try them all and see what works for you. Also enjoy the braodwater as quickly as you can - as the cruise ship terminal will change that area forever.
Sounder install. This is fairly straight forward (says a person who has installed a few now). Most go for the transducer inside the hull (shoot through) - the transducer can be either wet-mounted (glue a block of high-density foam to the bottom of the inside of your yak that has a cut-out of the transducer shape in it. Then fill the cut-out with a handfull of water and push the transducer down into the slot. The slot needs to be a snug fit for the tranducer.). In recent times I've gone the wet-mount approach, as I can then use the sounder in both my yaks. The other is the glued approach - where you put a big blob of Selleys All Clear etc. on the floor inside the hull and push the transducer down firmly into it and put a weight on it and let it cure (this is the permanent way). In terms of someone that you can pay to do this? Not aware of any companys that offer this - though most kayak sellers will do this at a price. Interesting that the Humminbird dealer said they wouldn't? Depending on where you live - I'm happy to give you a hand.
re Crabbing. Haven't done much of this myself (once I drop a few pots but got nothing). I think it's about having a flat area on the yak to sit the pots then go ashore and deal with them and the crabs. I've seen one chap build a floating raft (for want of a better word) out of pvc tubing that he sat the pots on and tied this to the rear of his yak and floated behind.
In terms of self help web sites for info on crabbing, installing a sounder etc. Have a look through the past posts in this Kayak section. Also go and checkout: www.akff.net and www.kfdu.com.au These have rigged kayak sections where guys have posted their "how to" info, which is really helpful.
Cheers,
Pete