Hmmmm "need" is a tough word to deal with... they only "need" what they need. Supplements may or may not be required to maintain best health. Generally speaking, they should get along fine as adults with good pasture, hay available to them, sheep minerals (most places are mineral deficient in the native soils), & maybe a small amount of grain as a health booster and training tool to get them to come when you want them to. You should be looking at their overall health and body condition to determine if they need something else.
They try to help us do what we don't know about. They will go after mineral when they need it (and they will) so that should always be free choice. We keep a small amount of baking soda available and those that get bloat somehow sense that they need it. Your question could take a couple of books to answer so more specific questions would help some.
we have a mineral block and pasture. we were wondering if that would be good enough to maintain good health. We have the ability to give baking soda, but dont know how / when to give it.
Loose minerals work better for us as it seems that the blocks wear the teeth some. But I would use what you have for now. We get our baking soda (Sodium Bicarbonate) from our farm center so it's fairly cheap compared to what you get in a grocery store. We use feeders on our gates and stalls that is about 18" off the ground in containers that we got from Tractor Supply. Some of ours are a bit higher with covers mounted over them to keep rain off. Ours are pretty easy setups but I can take some pictures tomorrow if that would help. The screw in containers were only a couple of dollars each.
We have mineral and Sea90 (also a salty mineral) on the gates in all of our main paddocks. The containers are only a few dollars at Tractor Supply or the CO-OP. The only caution with the way I mounted these is they need some heavy hardware since the feeder becomes a back scratcher also.
When we do get a blowing wind it is almost always out of the south so this one is mounted facing north. We haven't had any of them get wet and they have been up for 6 months.
The gate in the picture opens away from the sheep but if I have the paddock on the outside of the gate open, I can anchor it in place to serve both paddocks. There is also another mineral feeder on each of two gates at the other ends of this paddock so they can be made available to 4 paddocks depending on the rotation. Every paddock has at least one feeder and two in a couple of cases depending on how they are being used.