Stabilise your acquisitions by building up enough stacks to dissuade potential aggressors. the Danube makes a good frontier to Makedon's north as you can park an army at the crossings, while the Adriatic to the west can be easily defended with just a few ships) You will want to proceed until you reach a defensible border (e.g. Seize early territory by whatever means are necessary. The immediate goal for your campaign is therefore to:

You'll need to invest a lot of cash into your buildings in order to keep your armies paid, so you'll want to get your major cities to level 2 and 3 as soon as is feasible. Especially in the early game, the extra income can go a long way in building up your economy.

Speaking of which: loot everything you can. By the same token, feel free to bribe potential factions into non-aggression or trade, 10k may seem like a lot to give up (and a blow to your pride) but remember, that's just the income from one looted settlement High-ball them and then drop the asking price a few times until you are able to get a few thousand gold out of them just to do business. Exploit the bugged AI by asking for trade deals again and again - if the faction you are approaching gives a likelihood of acceptance as 'High' then this means you can extort money from them in order to secure a trade deal. Trade with everyone, even if you intend to declare war. This will give buffs to the city's income, pop growth or public order and drive efficiencies within your economy. Leave one-ship fleets and one-character armies as rulers of each city, and as they develop, make sure to improve their administration skills tree. Recruit every general, admiral and governor that you can. At the start of the game, the AI needs to recruit an army, while every settlement's garrison army also needs to build up to full strength over a few turns, so by merely launching an all out attack with little regard to survivability of your shit stack, you can steal a province or two early. For Macedon I'd wager these are the barbarian regions to the north and east. Recruit a stack of mercs and shit tier units ASAP and steam roll in your nearest viable provinces. Haven't played a Makedon campaign in a while (aside from the amazing Alexander campaign that I just finished), but my overall tips for a DEI playthrough would be to:

Rome 2 divide et impera tips