With regards to your first question, yes, loving-kindness meditation aids concentration because, well you focus on an object (or more) while (trying) to suspend every distracting thoughts.
Initially, mindfulness with breathing can be difficult because the breath is too subtle for the "over-active & over-stimulated" mind.
That's why you can use thinking meditations such as loving kindness meditation, reflection on virtue, reflection on Buddha, Dhamma, Sangha, reflection on death etc. etc.
Also, loving-kindness elicits positive emotions, which make the mind calmer and brighter. That's the reason why the Buddha praised Sila so much, and it's Sila that leads to joy, tranquility so and so forth which, ultimately, lead to concentration and seeing things as they are (vipassana).
Ananda:] "What, O Venerable One, is the reward and blessing of wholesome morality?"
[The Buddha:] "Freedom from remorse, Ananda."
"And of freedom from remorse?"
"And of joy?"
"And of rapture?"
"And of tranquillity?"
"And of happiness?"
"And of concentration?"
"Vision and knowledge according to reality."
"And of the vision and knowledge according to reality?"
"Turning away and detachment, Ananda."
"And of turning away and detachment?"
"The vision and knowledge with regard to Deliverance, Ananda."