A hds 7 is a nice little unit, if you don't use the sonar much or plan too, the split sona chart screens can be adjusted, so you can have a far bigger chart than the sonar side. You can set up multiple pages in many different configurations, you can have just charts with added info such as depth in numbers which can be moved anywhere on the screen and enlarged to different sizes. You can literally have dozens of added info on any page by using the add info in the menu. I have mine so it permanently shows speed, depth, time, eta, battery, fuel burn etc etc on every page.
As for transducers, I use Lowrance standar 200-50 and a 200-80 on another boat, both mounted externally on the provided brackets. These hold bottom ok but start loosing depth at around 700m. In average water to 150m they hold ok at speeds of 40 kms 27knots.
I find Lowrance easy to use but I've used them for many years and enjoy tweaking mine to get it setup how I want it.