Should I limit the time I do metta? Metta feels great. It is unconditional love on tap. So, could there be too much of it? It is addicting.
No, there's no limit to practising metta. In Metta sutta it is mentioned that the one who practices this can do it anytime and anywhere.

Whether standing or walking, seated
or lying down free from drowsiness,
one should sustain this
recollection.
Metta sutta

This is one of the four protective meditations (metta, contemplation of the Buddha, death and foulness of the body) and you won't experience side effects as in other types of meditations as well. You cannot practice breathing meditation when you are ill, like headaches and anxiety, it tends to aggravate the problem, but metta doesn't. Also, it is usually recommended to practice the four protective meditations before breathing meditation to reduce defilements.
The claim, metta meditation does not lead to wisdom is also not entirely true. In  AN 11.16 sutta it is clearly stated how a metta jhana can be used to  develop insight.

Then again, a monk keeps pervading the first direction with an
awareness imbued with good will, likewise the second, likewise the
third, likewise the fourth. Thus above, below, &amp; all around,
everywhere, in its entirety, he keeps pervading the all-encompassing
cosmos with an awareness imbued with good will—abundant, expansive,
immeasurable, without hostility, without ill will. He reflects on this
and discerns,
‘This awareness-release through good will is fabricated
&amp; intended. Now whatever is fabricated &amp; intended is inconstant &amp;
subject to cessation.’
Staying right there, he reaches the ending of
the mental fermentations. Or, if not, then—through this very
Dhamma-passion, this Dhamma-delight, and from the total wasting away
of the first five Fetters—he is due to be reborn [in the Pure Abodes],
there to be totally unbound, never again to return from that world.
AN11.16