The short answer is that whatever pace you can manage is fine. The slightly longer answer is that there is a benefit to going faster. The faster you go, the more similar looking kanji you’ll encounter (before previous kanji are burned). This will force you to really look at and remember the differences between those kanji. So I think one month per level is the absolute slowest you should go, if possible. For reference, I did about 8 days per level until around level 25, and since then I’ve been doing around 15 days per level.
If you ever want to do more than one batch of lessons a day, or want to easily get the right balance of lesson types, you can use the Lesson Filter script.
I did annual for a year and then switched to lifetime despite already being level 35 at the time. I did this because I wanted to slow down and focus on studying other aspects of Japanese.
At your pace you’d be best off getting the lifetime membership, if you can afford it and are confident you’ll continue using WaniKani. With that in mind, there is usually a $100 discount off the lifetime subscription at the end of each year. Additionally, unused subscription amounts will prorate additional membership purchases. So if you get annual now and then get the $200 lifetime this December, it’ll actually cost you less (about $260 instead of $300). Plus, this will give you 8 months to use WaniKani before the lifetime discount, which will give you plenty of time to decide if you want to continue with lifetime. This is all based on the assumption that there will be another discount this year, which is of course not guaranteed.
I don’t do as much as I should, but I am participating in the beginner’s bookclub. The book currently in the lead for our next selection has furigana above all kanji. So if it actually ends up winning, it should be reasonable for people with less kanji knowledge to read along.
An important aspect of pronunciation is pitch accent. I use this script and make sure I always pay attention to pitch accent when learning new words.