I have PowerBlock dumbbells which adjust from 5 to 125 lbs each...and have had them since the mid 90's.
I have three sandbags...35 lbs for warm-ups and cardio, 60 lbs and 70 lbs for other movements.
I have five kettlebells: 35, 53, 71, 88 and 106 lbs. I can use them singly or occasionally will use two different weights together to make the body compensate for an uneven loading.
(I also have olympic weights, but I've been concentrating on "functional training" the past several months to do something different.)
As far as reps...instead of the 6-8 I'd focus on when lifting heavier with olympic weights, I concentrate on reps in the 6 - 12 range, with an occasional foray up to 15 for something like deadlifts.
The biggest problem with dumbbells can be getting heavy bells into place for a given movement, so if you go with a higher rep range you can avoid potential pitfalls or injury.
There are many theories on strength training, but there is ample science backing the progress that can be made with the ranges indicated. Plus, I'm no longer looking at setting personal bests...I'm just trying to stay strong and fit until I breathe my last.
Sandbags are adjustable, but not something you would do during the course of a workout. Better to have a couple that accommodate what you intend to do.
I generally do between 3 to 5 sets per body part...so on the press for example, I might do a couple of dumbbell press sets, followed by sandbag lumberjack press, and then kettlebell press.
You can have some fun with it. You don't have to do everything in a completely regimented fashion.