The Lowrance will probably be the main draw. The manual for that model says 0.75A, so 5 hours is 3.75AH.
The LED lights can be a very small draw if you go with just what's necessary, or quite a large one if you go overboard like some I've seen!
I have the basic nav lights on my kayaks, red/green up front and white on back, each side a 3" strip (total of 4). That's plenty to be seen over a mile away even before dark, according to some comments I've received. Only draws about 150mA, so in 5 hours uses just 0.75AH.
Some of the fishing kayak LED kits people have installed around here have several FEET of LED strips - the things are lit up like Times Square! They draw considerably more power.
I bought my batteries at Batteries Plus. Just the basic AGM sealed lead-acid battery. They have an incredible variety of sizes and shapes to choose from, check prices as they'll have two same-capacity batteries priced quite differently. For instance, the one that fits an APC UPS will be considerably pricier than the one that's just a cube even though they're the same AH rating.
I also use the Battery Tender Junior. Excellent and simple device for keeping these smaller batteries charged.