What is IUPAC name of $\left(\mathrm{CH}_3\right)_4 \mathrm{C}$ ?

Which functional group from following is considered as principal functional group if polyfunctional compound is to be named by IUPAC system?

What is the number of $$\mathrm{sp}^3$$ hybrid carbon atoms in $$\mathrm{HO}\left(\mathrm{CH}_2\right)_3 \mathrm{CH}\left(\mathrm{CH}_3\right) \mathrm{CH}\left(\mathrm{CH}_3\right)_2$$ ?

What is IUPAC name of following compound?