I try to figure out how to make an imperative sentence in Latin with the following.
Boys, be ambitious.
Is it possible to make it by using 'esse + adj.' as English structure indicates 'be + adj.'?
Pueri, este ambitiosus.
And how can 'Love myself less' be translated into Latin?
the imperative sentence “Boys, be ambitious” translates as :”Pueri, este ambitiosi” or better “Pueri, estote ambitiosi” with the future imperative “estote” (2nd person plural) instead of the present imperative “este” (2nd person plural).
The verb SUM, in fact, often uses the future imperative instead of the present imperative, just like the verbs SCIO, MEMINI and HABEO (in the sense of "I consider") that regularly use the Future Imperative instead of the Present.
Please note that you wrongly used “ambitiosus” in the nominative masculine singular instead of the correct form “ambitiosi” in the nominative masculine plural agreed with the masculine plural “Pueri”.
As for "Love myself less", such an imperative sounds quite strange whereas it would make sense if you said:” I'm happier when I love myself less".
In short, is this imperative “Love” addressed to a person that you ask to love yourself less?
If so, "Love myself less" would be "Me minus ama" which however sounds a little bit odd.