Just about every discussion i get notifications for is deleted , what s up with that?

I started my PhD when I was 34, I say go for it!

Maybe explain the gblinear version of xgboost? You only explained gbtree

You can get fully funded for phd. School paid my tuition and gave me a stipend

Why do all these posts get deleted? And where do they go?

When you downsample try to get at least 1:10 ratio (minority:majority)

5% imbalance isn't bad. Just use a cost function that uses a metric to handle imbalance. Ie, the weighted average binomial deviance and you'll be fine.

Also you can create downsampling ensemble to compare performance and compare. Don't downsample to 50/50, try for at least 10%

You've got a good problem, lots of observations with few features

Regarding 2, there are only 500 features, dimension reduction not needed.

1 and 3 are last resorts

Yes

Its more like a toolkit than one method that works better than the rest. Don't forget to add an auto encoder to your list

Easy, use all the training data, use smaller label weights for the uncertain data. But keep in mind, if the data is uncertain how can you trust it??? If you say the label is uncertain is there a probability that the label is incorrect? How will you measure performance on your uncertain data vs certain? Boosting algorithms will certainly overfit , it will be difficult.

Why was the original post removed? In fact most of the posts I get notified for are actually removed....?

Is that just an 'automatic' grid search?