>>2430841Weighted line (lead core) is the cheapest (initial cost) way to troll deep at lowish speeds in still water. I prefer using a line counter reel to trying to remember what color is what depth. I have some Okuma Magda line counter reels on cheap (Berkley Cherrywood) casting rods loaded with lead core. To help make your spread a little "bigger" I recommend using two different weights of lead core (which creates different trolling angles) and two different lengths of rod (which creates a natural difference in distance from hull). I have two downriggers on the back of my boat as well, which get the baits down much quicker off of the end of the boat than the lead core does, which allows me to fish 6 baits spaced far enough apart that you don't really have to real them all in when one hooks up unless you hook a monster and it decides to pinwheel its way in, but if you don't want to invest in downriggers, you could fish 4 lines just fine with lead core, and maybe you could get some big 3 piece 12+ footers to widen the spread further if you wanted to run 6 lines of just lead core.
As for the sonar, If you think you'll ever want to get into trolling motor automation (even if it's on another boat in the future, I recommend Humminbird. Sure, you can get most or all of the functionality of the Johnson Outdoors I-Pilot Link system from other brands, but it's either going to wildly more expensive (Garmin) or a bunch of adapters and hacked together systems (Lowrance). If you're sure you will never need that, pick the sonar features you want (high resolution, side imaging, 360 imagining, steerable imagining, etc) a screen size that makes sense for the space you have (be warned, however, the Helix 8 is the same case as the Helix 9, but with just a bit more bezel).
Garmin Echomap Plus 43 I use canoeing is great, but I chose it for its smallness, and if you want a bigger screen, there are more economic options from Lowrance and Humminbird.