Biomass Regression Equations, some questions

#1
Hi all! Thanks to everyone who contributes here it has been so much help so far, this forum is full of useful advice.

I have some questions with regards to biomass equations, also loosely termed allometric equations. I am looking for relationships between :
- Total biomass (dependent) and RCD (there are other explanatory variables also I could explore)
-Total Leaf (dependent) and RCD (there are other explanatory variables also I could explore)

Here is the dataset: https://drive.google.com/file/d/1G00HXF4hj6_Ka9_T4Izo5sAsPaEzwkZq/view?usp=sharing

My questions are regarding the SPECIES = "IE"

I use the package R, I have done normality testing, transformed total biomass to square root, then done some linear regressions on this data and robust regressions using the package MASS (Hubert and Bisquare), but I think I really lack the theoretical background to make confident decisions as to how to handle this dataset, and honestly I can say I do not know what I am doing, just flicking from one tutorial to the next online but not grasping much.

Question 1: My data are not normally distributed and have outliers, the outliers are not errors in the data but an artefact from some trees having high biomass. Is there a form of nonparametric regression that I should consider for this data? I've read a lot about Robust Regression, but I do not know if it is appropriate for non normal data or for transformed data.
Question 2: Would it be appropriate to use a square root transformation to normalise the dependent variable? (in this case, total biomass)
Question 3: Is there anyone on here with time to do some sort of mentoring with me on this dataset? I'm in the last couple of months of my PhD and my supervisor suffered a stroke. I've never done anything like this before and I'm really lost

Thank you! :) L