Hi, there!
For the record if not directly relevant anymore: I think arguably the smoothest experience will give us the Digital Pāli Dictionary (DPD) of Ven. Bodhirasa (South Africa), which he still updates regularly. It includes various details not found in any other dictionary. It runs via Golden Dictionary and MDict. Detailed instructions on how to set everything up can be found via: Home - Digital Pāḷi Dictionary. If you want to receive updates, please PM your e-mail address, and I would forward it to be included in the mailing list.
The good thing about Golden Dictionary is that you can also add the Critical Pāli Dictionary, the PTS Pāli-English Dictionary, Concise Pāli-English Dictionary, Dictionary of Pāli Proper Names and some more. The first can be downloaded via: https://drive.google.com/file/d/1qJOcJ-_SjJu0e2ilyc4-yN2SsEHaBMuh/view?usp=sharing, the other ones via: Release Second release · simsapa/simsapa-dictionary · GitHub. The net result looks like this; the entry for the different dictionaries all lines up neatly:
For learning Pāḷi in general, I also warmly recommend using, alongside with what is outlined above, grammar guides identifying the meaning and grammatical from of each word, thus leaving much of our nerves intact. For the sutta you mentioned, there is, for example, Ven. Ānandajoti’s Tisuttanirutti, which provides a grammatical analysis of the Metta-, Maṅgala- and Ratanasutta: A Grammatical Analysis of Three Discourses.
I can also recommend the grammatical analysis of the whole of the Dhammapada: http://buddhism.lib.ntu.edu.tw/BDLM/en/lesson/pali/lesson_pali3.htm.
For getting a convenient grasp of the grammar itself, I furthermore would recommend the Pāḷi grammar Māgadhabhāsā (Pāḷi) – A Compendious Grammar on the Language of Pāḷi Buddhism (Second Edition):