According to Ripple the url https://ripple.com/wiki/Gateway_Integration_Manual for the Gateway Integration Manual is "DEPRECATED". Ripple says "This page has been replaced with the new Gateway Guide on ripple.com. Please refer to that document instead."
Here is their newer doc: https://ripple.com/build/gateway-guide/
Ripple does not prohibit those who are not "banks, funds or other financial institutes" from building a gateway. Just the opposite. It is in Ripples' best interest if widespread (Ripple compliant) adoption is made. In their example Ripple uses "a fictional online currency exchange named “ACME” and its users as examples, to show how ACME can expand its business to include being a Ripple gateway".
Businesses that link the Ripple network to the rest of the world such as "online financial services, such as payment systems and digital currency exchange" are businesses which could build a ripple gateway.
Looking at the list of Ripple Popular Gateways shows some of the types of businesses which could become gateways:
These include Panama Bitcoins (http://ptycoin.com/ripple), SnapSwap (https://snapswap.us/ and https://snapswap.eu/), and LakeBTC (https://www.lakebtc.com/) amongst many others.
To answer your query about "AML policies and require KYC information" the specific compliance regimes for this depend on the jurisdiction your ripple gateway lies within, and where your customers reside. For example if your theoretical Ripple Gateway was physically located within the USA then American AML KYC legislation would apply to your business. The same would apply if your gateway was outside of the US, but traded with US citizens residing in the USA. Other jurisdictions will have other legislation. Many crypto businesses have implemented their own brand of AML KYC specific to their own jurisdictional requirements.
There are more countries which do not have definitive crypto legislation than countries which do, so the applicability of traditional legislation itself is even in question for example the lack of a definition of what bitcoin is in each country can create a situation in which it is not clear whether or not legislation including AML or KYC applies to cryptocurrency, or even more undefined internationally, Ripples' legal financial exposure in transferring value globally in affected countries. This will be different in each country.
To answer your question "what is the minimum starters level of capital need to make own gateway?" the level of capital required would depend on the nature of the market you intended to serve. Different markets would require varying levels of financial commitment, the depth of the trust line you wanted to maintain would affect this, and the scope and geolocation of your organizational and technology infrastructure would also come into play.
Overall, it is highly beneficial to understand the law in each jurisdiction your Ripple Gateway will do business in. The opposite is also true.