I'm just wondering how to handle the capital gain tax between me and my partner.

Both partners have capital to deploy.

I simply budget 5% for capital expenses and 5% another 5% for maintenance and work with the money that accumulates in that pot.

You wire funds to a company that is in the business of building buildings, they create plans, get permits, raise additional capital, supervise construction, supervise filling the building with tenants, sell the building to an institutional investor, and if everything has gone to plan then there will be a significant profit and they wire you back more money than you put in.

Will a lender still need to look into personal capital etc? 

It was a slow start to the initial spring 2024 shopping season, but properties are still closing quickly, still nearly 1/4+ for all cash and the majority of investors are well capitalized due to the appreciation of their real estate and stock based assets. 

I want to capitalize on opportunities that other investors may miss out on or just have missed.

Consider reaching out to lenders that specialize in investment properties and can move quickly to capitalize on the current market conditions.

No start-up capital, no reliance on banks, no particular expertise required (initially at least, we had still had to learn a lot along the way!).

You likely still would owe capital gains tax on these.