The g++ not found thing is a warning that is safe to ignore.
The cannot allocate vector has come up before but I’ve forgotten the exact solutions.
Some people have luck clearing out R configuration files: Cannot resolve the "cannot allocate vector of size … " error and here’s someone who got past these problems by recompiling their models: Error: cannot allocate vector of size 17348.7 Gb (you can ensure this happens by changing the model file name to make sure and not get a cached binary).
Give those a shot and report back