Welcome, Shri S,
It is clear you have done much research and are working on being in great physical shape. That is a big step toward succeeding in your climb.
Here is my first thought regarding your line:
6. I probably don't have the level of fitness and experience required to do the Mountaineer's Route even with a guided group. With your fitness and experience, you are a prime candidate for a guided group. Guided groups are about the only ones ascending Mt Whitney in April. Nobody will be trying the Main Trail in April.
The snow will be deep and soft at that time, especially if this El Nino weather pattern we are having continues. Since you will be alone, you will be trying to break trail through miles of soft snow -- pretty much impossible for a lone hiker. If you were in a group where the front man could break trail for a while then rest and let someone else go, the group would have a more likely chance of succeeding.
That is why you should go with a guided group. Multiple people can help each other break trail. They do the Mountaineers Route because it is shorter and more direct, with fewer miles to break trail in soft snow.
Please check with guiding groups.
SMI and
SMC are two to start with.
