I'm hoping I can get some advice/help on this

Here's the situation:
I am a US Citizen and will be in the UK on a tourist visa.
I plan to apply to 'remain in the UK with Family visa' as I will be in the UK and my partner is a British citizen and currently employed. (£13,500 salary )She has never worked in The Netherlands.
We do not have a formal civil partnership however we have been living together over the past 2 1/2 years with proof of joint bank accounts, tenancy agreements, NZ Partnership Visas, History of past texts, photos, etc. My question is:
Would this satisfy visa requirements?
Am I able to choose the '2-year route?
Is there still that £18,600 minimum financial requirement? If So, would assets count towards that minimum threshold? (High value personal assets of £10,000+)
Thanks again for your help. Your efforts definitely do not go unnoticed and are certainly appreciated.