Telescope in Sun's gravity lens focus - pointing, gain, distortions
The pointing is not a fundamental problem with the suggested design: The suggested trajectory is designed to include a Sun flyby as the last flyby. This ensures an asymptotically radial trajectory away from the sun after the flyby, hence maintaining the pointing relative to the sun. The proper motion of the observed object may be some challenge, but the trajectory could be adjusted appropriately by an additional burn.

114 dB are an amplification of a factor of about $2.51\cdot 10^{11}$.
It doesn't refer just to the magnification, but to the intensity of the signal.
Therefore interferometry with a long baseline isn't the same; the latter provides a high resolution.
Whether those numbers are achievable in practice is a different question; a factor of 1000 for naturally occuring gravitational lenses would mostly be regarded as excellent.
Theory allows arbitrary amplification for perfect alignment of observer, lense and observed object.

Most of the distortions can be deconvoluted, revealing the field of gravity of the sun, and the shape of the observed object.

Gravitational lensing is used today, here some lecture notes, and here quasars as an example.