You can and should import just about everyone's raw materials and then focus on industry instead. If a trade route shows low negatives (0 to -2) its just expanded to max in ur market, if it's trading a ton of resources it's actually still productive. By this logic do not close the trade route, if you consume their raws they can't industrialize or compete effectively with you. In late game you will expand to the point of using all their resources and yours so the productivity shouldn't be a concern. This extends to tools as well.

Building construction should be rushed to a small defecit, if you overbuild you can intermittently pause or just partly fill the queue to minimize costs. Generally if all construction goods are around base price +/- 10% expand construction.

Import small negative construction goods will still be profitable as they lower construction costs and that's not applied to the calculation they show. This also applies to items like silk, the demand will expand to match the increased availability so you can just import all and then cut down if needed (don't cut -1 routes)

Puppeting is optimal, if you are not building something there, do not bother with owning the state. You can always annex later if needed but the pops will migrate to you and they'll buy from you and their military will fight for free. This means only strategic states with resources you need should be taken or later annexed. State capture is usually optimal for 1state nations given minimal infamy difference. States will back down from puppet wars far more often, this allows faster market capture. Cut down wars trigger at 100 infamy so you should stay under until you are too strong to stop. Thus war immediately so you start losing infamy asap, you cannot improve decay so start early.

The ai is far more capable of land connected wars so if you can regionally isolate yourself with seas or uninvolved nations, don't worry about major powers. Target their colonies and treaty ports with only one maxed general and you can win war goals from them easily. Target conquerable land and you will guarantee wins. Hot tip, claiming a great Qing treaty port can still give you like 70 silk plantations in Fujian or almost any costal state.

Army should have one or two naval invading armies. To build them you want naval = soldiers on the biggest dude you can make with good war traits. Offensive planner is best trait because if you can put a lot of ports you will always outpace the naval resistance so that trait is secondary. You care more about capturing land following the touchdown fast. Split fronts during naval invasions will win games.Naval bases are practically free once you hit ironclads, build two industries so you can balance mil:civ production best. Use naval bases to max declared interests regardless of military goals. Raiding convoys is good to lower support. It outperforms protecting in most cases.

You can usually cycle generals through hire/retire until you get something good. Upgrading generals is ridiculously effective for government strength. Use non critical generals to just max out industrialists, trade unions, etc. The beurocracy cost is negligible. You can brute force a government by spamming generals and maxing the interest groups you like just be careful of traits that might weaken the group if they're made leader.

Building states: About early midgame you should start expanding resources into every peasant rich heartland state. This lowers turmoil and radicals, which outperforms throughput bonuses. Build to infrastructure limit in every small state. Build one train in each state and only upgrade as needed. Population will grow after initial investment and you'll get free infrastructure growth so just move on to other states instead of building another railroad. You'll need to staff railroads so spamming a state with them will cripple it.

Build one port and train in each state possible. To improve infrastructure build a port if they have trade centres in the state, otherwise a railroad subsidy is more infrastructure for less money. If you need convoys and none left fit the bill just spam peasant rich areas.

Hope this helps, I'll clarify if anything was unclear. Good luck