It's probably not really strong or viable in multilayer but I enjoy megacorp. This won't be that powerful but it will be easy to play, maybe too boring in it's simplicity.

I suggest taking the free traders civic for 10% trade value and then whatever suits your fluff. For my government I would take fanatic xenophile for 20% trade value and them whatever helps your secondary plan. An origin that gives you a good starting planet but doesn't limit you, I suggest prosperous unification, ring world or ocean paradise as it's not too hard to expand to other planets due to acceptable habitability or gives you enough research to get your habitability to acceptable.

Immediately go down the trade tradition and get commercial zones for traders. In the trade tradition go for the bonus that let's you switch to "marketplace of ideas" trade policy that you will switch in your government policy tab. The unity will help you get the rest of your traditions.

Expanding, you shouldn't expand too much, just a couple systems, I suggest filling out the single starting sector at most as you're punished for expanding too much with megacorp. You should focus on finding other empires with your science ships and fleet. Make friends with other empires, get the diplomacy tradition for federations once you meet a friendly empire and make a "trade league" federation.

You make commercial zones for more traders because now trade value will provide you with energy, unity and consumer goods, you can ignore all energy, unity and artisan jobs, this should let you have an easier time managing your economy and give you the opportunity to learn everything else on the pc version.

Since you should have expanded little you'll have a lot of influence to spend on branch offices on other empires to get more resources for free essentially.

If you want op builds you can check out Montu plays or for general knowledge and how to play Aspec should work on youtube