Localizing traffic using BGP

Hello all,

BGP design question. My scenario is very much like an online gaming
company with servers on multiple continents.

Details :
1. I have datacenters/servers in many POPs globally.
2. I am a stub AS with multiple ISPs available at each POP.
3. I do not have the resources to buy dedicated fiber to link these
POPs, so my backbone is essentially a bunch of VPN tunnels.
4. I own a /21. Of which I announce /24's.
5. I have a mechanism to allocate client sessions to any ONE of the
POPs based on network performance (which is what I want to optimize).

Questions :

I presently announce different /24's out of different POPs to
localize traffic. All these prefixes are announced from the same AS
number. This obviously can't be best practice. Are there any published
BCPs or RFCs tackling this issue ?

Is it recommened that I get multiple AS numbers and announce
symmetrically from each "smaller" AS ? Or should I announce
inconsistently from different locations ?