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It depends on your language, how you perceive the Japanese /ɺ/. It is more similar to English L than R acoustically because the English R is not tapped but a retroflex (or similar) approximant. Similar for speakers of languages which use guttural Rs. But in languages where R is tapped or trilled (the actual IPA /ɾ~r/), /ɺ/ sounds more similar to R than to L.
I'm not fully aware of all the nuances, but going into the extreme either way would come across as forced.
Regarding P, /p/ was a normal phoneme in Old Japanese, but it weakened /p/>/f/>/h/ historically. Hence also the alterations in compound words where words starting with H will change to starting with B (you should know this from sumo; a sumo stable is heya but in names it becomes the suffix -beya). However it remained /p/ when doubled (e.g. seppuku) or prenasalized (= after moraic (syllable-final) N) (no examples off the top of my head). Otherwise /p/s come from Chinese and later European loanwords.