With humans in a normal environment this strategy is ridiculously efficent.
I'm trying it out now in an Ugnari/600K research/Many Monster/Many Pirates 1400 map and for the moment, while a little slowed down, it seems to work.
Make friends with everybody: pay them at first sight 10000 (if you have it) and repeat every time you speak with them and no other exchange has been made. When they become friendly propose a Free Trade, when they become delighted propose a Mutual Defense.
When/if you got a rare good share it with everybody.
Work hard on your reputation: no spying, keep a few spy for defense purpose.
To keep your military happy unleash them against all the pirates around (good for your reputation also).
IMPORTANT! Just ignore all the unfriendly suggestion from your advisers. Unfortunately not all of them so be really attentive. The wrong click can wreak havoc to your reputation.
Ignore also trade embargos or war queries from your allies.
Buy all the techs on the market and sell them to everybody. Work your way toward the really expansive ones.
I usually just keep to myself the colonization ones and the maps unless it is really necessary.
When your finance/tech advance is solid buy also any disputed but buyable planet and base.
When you feel in a pinch you can sell them too.
Colonize everywhere. From 100% to 50% Quality and even less if there are ruins and interesting resources.
No free planet can be left without a colony ship icon.
Extras to pass the time:
Explore any interesting place and fill your navy with early capital ship and a pair of Worls Destroyers. For to do that and for your economy buy a lot of Constructors.
I'm not sure if they are really needed but starports and defence bases can be a good place where to put the overflow money that came with the tech trading.
Place a few bases in the Ancient Guardian system: If the Sakature War starts they will become allies and you will exchange the bases (or the planet if you were lucky) for an enormous amount of advanced techs.
BTW when the game start I immediately go in the ship design panel to double the warp drives for the Colony Ships.
Just hope for the Sakaturi to show up for a nice Great War to end the game with style.
Unfortunately with just 33% of the Galaxy planet needed to win that can very well just not happen.
I will not be disappointed if a future patch expansion will limit or even better kill this strategy: it is too mechanical and repetitive, but at the same time too efficent.
There should be more drawbacks if you don't help an ally in a war on in a trade dispute.
Also being ally of two sworn enemies shold be more difficult.
If you accept to go to war or trade embargo someone you should somehow be obliged to keep at it for some times.
The AI should be capable to not exchange a strategic technology or at the least it should up the price at crippling levels and should know when it is not strategic anymore.
Maps also shold be more valuable and more difficult to buy (I still think that you should not be able to see behind nebulosae and not in real time if you have not ships or monitoring station in line of sight).
The Galaxy is also too flat: there are not choke points, no real geography, no real need to think about the topology of your expansion.
The techs are too many and not enough relevant, you are becoming stronger but the single techs are more bargaining chips than a real advancement of your civilization.
Planets should be more relevant also. Abitable planets even more so (and rarer). Expecially the first colonies, the core of your empire, or the really special ones (Dune, Trantor, etc.)
Victory condition should be more of a combination of factors: 33% of the galaxy planets (or 50% if you want make it more 'difficult') is too simple and slightly meaningless.
Planets, economy, happiness of your empire, techological prowness should be combined to force a more balanced strategy to win, even pacefully.
From the Regina subsector to the Sakaturi base... a long and fulfilling trip.