working holiday visa

Hey there! I'm looking to hopefully apply for a working holiday visa next year. I have never applied for a visa before so all the information is quite daunting! Just a few questions (for now!). I was wondering how to plan flights in accordance with the visa being issued. So, do you book the flights before the visa is (hopefully) issued? If so, how long to leave between the flight to Japan and the visa issue? Also, does the 12 months of the visa start at the time of issue or does it get activated once in the country? I hope these questions make sense, and many thanks in advance for any information and advice anyone can provide!

I would book the flight after you hit the COE or the visa. It is a myth that booking fights very early is cheaper. Specially if you have some flexibility. Plus there is always the risk that your WHV is not granted.
Itfs 1 year of staying in Japan.

"visa" is "entry permit", not "staying permit".
many people use it wrongly. and they misunderstand the immigration system, because of that reason.

you will get a "visa" of working holiday. it is valid only for 3 months (the term may be longer because of the virus pandemic right now.) within 3 months, you need to come to Japan. when you land to Japan, the immigration gives you a permit of "one year staying", because of the reason of working holiday.
once you arrive in Japan, your "visa" is consumed, and becomes useless. i.e, you will get "another permit" of "staying in Japan", so called as "(resident) status", έ—―Ž‘Ši in Japanese. you may stay in Japan because you have a resident status (not because you have a visa).
one year is not the valid term of "visa", it is the valid term of "resident status".