Hey bud some good tips have been mentioned but there are a few you really need to be carefull of.
Using braid can be very dangerouse in a rib or sib ( it's pretty much all I use though). If your line gets snagged in the bottom or you hook a good sized fish that pulls the braid against the tubes under pressure it could slice them open like a knife.
The strengths people are recomending are also extremely strong and would be almost impossible for you to break if you get snagged in the bottom. My heaviest braids that I use on large tuna and marlin etc are 50lb, my most common size used is 10 lb which will handle drag settings on the reel of 6-7 lb and capable of stopping most of the smaller tuna species. Spin reels are more than capable of taking on almost any big game so don't just look at multi's, I use spin gear on marlin and tuna with great success.
Braid strength labelling is very misleading, many 10-20 lb braids break well above their stated strengths, often more than double, have a look here at testing
Paulus Just Fishing
Fluorocarbon is a waiste of money in my opinion, I've tried many brands side by side with plain mamoi diamond mono and have found the plain mono outfished the fluro in almost every ocastion. I've also taken samples to 36m on scuba to see if it becomes invisible to the human eye, it doesn't. I've also searched to find any scientific research on the relationship of fluro on fish eyesight with no luck. But if you feel more confident using the far far more expensive fluro then go ahead as there's nothing better than fishing with confidence.
Over to fish finders, these can be a vital piece of equipment where pretty much the more you are prepared to spend the better fish finding they tend to be. In saying that even budget models should show fish and bottom conditions clearly, even an old Lowrance hds 5 I used to have picked up my 1oz jig heads with soft plastics dropping into snapper at 56 m. That same unit clearly showed bottom in 600m of water.
Things like sidescan and 3D scanning will actually show the shape of fish and clearly show features of wrecks etc depending on depth. Most sounder manufacturers are very competitive so it's hard to wrong with modern models, just do a little research. As for transducer mounting, I'm sure with a little thought you could find a way to fit one, I use external mount types and removable ones on my Kayak.