can this tree be saved...
This depends on many factors. Your USDA zone will be important here. Some magnolias DO lose their leaves in cooler climates. Many do not, even in the coldest locations.
Can you give me a little more information about your area, and the tree's environment? A photo will help greatly as well.
My magnolia tree has developed brown discoloration on the leaves and even darker brown spots. They are not on the back side of the leaf. The tree was planted about 7 years ago.
These are fungal spots. This is common, and usually not a big threat to the tree. This will usually resolve itself over time. You can help it along some with some wettable sulfur. Just follow the instructions on the package.
This article will give you more information: https://www.gardeningknowhow.com/ornamental/trees/magnolia/magnolia-tree-diseases.htm
Tree is losing leaves and the limbs are getting brittle and coming off. Plus there are blottes on the branches
Can you include a photo? This could be a serious fungal infection. As a preventative measure, and a spot treatment you can use wettable sulfur in the soil around the tree. This can help kill off an infection, and will replace sulfur deficiencies in the soil.
My Japanese Magnolia tree has bloomed prolifically for years. But last year and this year, the blossoms are fewer and less robust looking. Could less watering because of Ca drought regulations be killing the tree?
Here is an article on magnolia blooming problems. Get a soil test from Cal Extension Service. https://www.gardeningknowhow.com/ornamental/trees/magnolia/magnolia-blooming-problems.htm. It drought by itself caused the problem, I believe you would have seen leaf curl and leaf drop last summer during bud formation. If yours is simply not making buds in fall, nutrient deficiency may be to blame or you may be growing it outside the recommended zones 5-9. Look up your AHS Heat Zone. This magnolia is rated for 9-5 but the ag and AHS zones are different. http://www.plantmaps.com/interactive-california-heat-zones-map.php
Am I right to say same soil type as you would for rhododendron?
They will do just fine and slightly better if you growth them like you do rhododendron. They are very tolerant of most any soil type, but they do like to be in slightly acidic soils. So Yes, I would say that you are correct.
Two large branches tore off my deciduous magnolia tree because of heavy snow/ice. The parts of the branches that are left are jagged. It is still cold in New Jersey. What is the best time to cut off the rest of the branches that are left and should I cut them back to the trunk?
Remove the damaged branches as soon as is safe to do so. A jagged cut is an invitation to disease and bugs. If the limb meets a branch(lateral) at a Y and the branch is at least 1/3 the diameter of the limb, you can trim back to the Y. If there is no such branch, take it back to the main trunk. Please read up on "branch collar". It is imperative that you make the cut properly or the wound may not heal. There are YouTube videos and google images of branch collar cuts.
I bought a red magnolia that was sold as being able to grow on a patio in a pot , so not too high. I have had this one for 4 years and it has not flowered. It is perfectly healthy and is decidious but only produces leaves. It is in proper soil for magnolias.
You should fertilize this at least once per year. This is likely the cause if it doesn't get fertilized regularly. I would also add dolomitic lime to keep the pH stable. This can help it along as well.