My progress in WK was very stop/start until I started using the [Userscript] WaniKani Lesson Filter - I found the mental workload of doing batches of nothing but kanji over several days a bit much, so this filter allows the user to set their batch size and the number of each of the item types to best suit their needs.
As you have stated that a timeline of 5 years is acceptable, and as there are about 3 times as many vocab as rads/kanji, doing a daily batch of 2 rads/kanji : 6 vocab (or if too much, 1:3) should keep you ticking along nicely.
Choosing the time you do your lessons so that you will almost always be able to hit those Lesson+4hrs & L+12hrs reviews really helps.
Best of luck, and good on you for getting back on the proverbial horse! 