All depends on how much you want to:- spend, cut & chop + what you already have in place. To get NMEA 2000 data from your engines to the helm will involve running a cable from each engine back to the helm. Depth/fish/sonar will involve a transducer & its cable. It's one of those jobs that grows. Start chucking in vhf/AIS/RADAR & before you know it you've rewired the boat & sold a kidney
As for brands, the main consumer brands seem to be Raymarine, Garmin & Lowrance. I've got last generation Raymarine & can't say that I'm over impressed, when it works it's fine, but it can be flaky. I had Lowrance on the last boat & loved it, I should have stuck with Lowrance on this boat IMO. I've no experience of boaty Garmin gear, but I have a handheld as a backup with the G2 vision chart, I prefer Navionics charts as they are identical to "proper" admiralty charts, the Garmin ones aren't IMHO.