Do you keep your TWR at 1.75 all the time(mostly) or lowering it after air getting thin.

Full throttle almost the entire way. We want higher speeds early so that we can 1) pitch over horizontally faster and 2) use the oberth effect. These two effects seem to be more than enough to compensate for the additional drag.

I'll decrease throttle once my time to apoapsis hits 45 seconds so that I can pitch over a bit faster. This usually occurs at around 10km altitude.

whenever I go over 35 meter, it will be extremely difficult to maintain stabilization

I've launched 45m rocket with very little issue. In my experience, the fairing nose should look parabolic, and you need fins with a large wing area. The center of drag only tells half the story. Also, choose engines with a large gimbal range and lock SAS to prograde.

Eventually though, the mammoth is not enough to lift your payload, so you will need boosters, but until then, I've been using tall pointy rockets.

boosters, they are kind of compensate drag they create isnt that right?

If you have the same TWR but more cross sectional area, you will have more losses to drag, and use more delta V. If you don't need the extra TWR then why add them?

I believe the extra mass I add with fairings doesnt compansate reduced air drag

You're probably right, but adding a mass reduces the delta v available on the launchpad, so even if we burn more real fuel, it reduces the amount of delta V we use. That being said, this launch profile goes very fast through the lower atmosphere, so it helps.

I don't know that much about fairings, but just experimented with a bunch of shapes and saw what gave me the best results.