I've been happily living in the UK since March 2018. I came over on a spousal visa and I'm not sure what needs to happen next.
I thought after two years I could apply for ILR but when reading the gov website I got a bit confused. Is it actually five years? My BRP expires in 2021... How do I go about renewing it?
It used to be 2 years, but that changed on July 9th 2012 and now it takes 5 years to qualify for ILR. The spousal visa is only issued for 2 years and 9 months, so you need to apply for an FLR(M) extension visa for another 2.5 years before you can apply for ILR.
The earliest you can apply for FLR(M) is 28 days before you reach 30 months (2.5 years) in the UK, and the latest you can apply is the expiry date of your BRP. If you arrived here in March 2018, you will reach 2.5 years in September 2020, so you likely can apply any time from August 2020 (28 days before the date in September when you will reach 2.5 years).
The application requirements are the same as for the spousal visa, but instead of providing evidence of communication during your relationship, you provide evidence of living together for the previous 2 years - so you need to make sure you have mail in both your names (either joint or separate) for every 4 months for the 2 years prior to applying (you need 6 documents in each name, every 4 months, from at least 3 official sources. They must be mail delivered to your house, not issued online).
See here for applying for FLR(M):
https://www.gov.uk/government/publications/apply-to-extend-stay-in-the-uk-as-a-partner-or-dependent-child-form-flrmI've been a bit hung up on not becoming a UK citizen- but after doing some reading over in the tax section I've decided to try for it. I dont really think that changes anything on my path at the moment as I am looking to be here permanently anyway- just thought i should mention it
No, it won't change anything now and isn't relevant at the moment. You must hold ILR before you can qualify for citizenship, so you'll need to focus on the next 2 visas (FLR(M) and ILR) first, before you even need to think about UK citizenship.