Yes you need to get the form from JPN (the one for marrying outside of JPN office), then fill up the form, get it stamped by a commissioner of oaths and then submit the form together with your partner at the JPN closest to either one of your addresses.

Once that is done, bring the form over to your association, temple or Church.

@deedeee is right, you need to go JPN first and fill up some borang (can't remember). Need passport photo(but please check what colour the passport photo needs to be in, I can't remember too, sorry). Then, will need to get a stamp from commissioner of oath, cost a little bit of money, I think a few ringgit? I went to the one near Hartamas last time and they do have commissioner oath there so I can settle one shot. Sometimes he/she may not be there so it really depends on your luck too.

And yes, register through association DOES NOT need to change IC, but for temple, at least one of you must be Buddhist (as per IC). Believe church wedding is the same too.

Can't recall already. If I remember correctly, I approach the temple for guidance on what to do. They are able to guide me accordingly. Perhaps you can check with the temple you engaging.

After submitting the form to JPN you have a 6 month window of validity, I submitted end of September for my ROM date at the end of November, so your timeframe is possible.

You can check with the association first to see if there is a slot, the slot won't be confirmed till after the JPN submission is done, based on my experience.

Can't recall already. If I remember correctly, I approach the temple for guidance on what to do. They are able to guide me accordingly. Perhaps you can check with the temple you engaging.