Just loaded the save. You are incredibly weak for what you should be. If Austria invaded you would have maybe 5 minutes at a medium speed until you would have to surrender. Your army is 1/3 of Prussia's, but your forcelimit is larger than Prussia's current standing army. You're at 54 units, but your forcelimit is 199. Why you don't have your military to the max is my main question. But even your army at your max forcelimit would be unable to meet about half of Austria's, but you and Prussia combined would have a decent chance of not getting absolutely destroyed.
You are holy roman emperor but in the next election no one will vote for you, you have no other option but to keep your place as emperor as it gives a large manpower and forcelimit bonus. I also noticed that you are excommunicated, which is never a good thing. So you'll want to avoid that by keeping your relations with the papal states above 100, at this point you have more than enough money to do that. Also your infamy is rather high, so I strongly recommend that you build an embassy soon.
However, your relations with Austria are pretty decent. Royal marriages and giving them military access (both "Very Likely") would be beneficial to boost relations and give them a stability penalty for invading you. Since your relations are decent there will more than enough time to get an economic powerhouse going and becoming stronger than Austria (you have, after all, the second largest economy after Austria). Don't wait too long to build up, if you're going to become a large nation all your relations will quickly plummet and everyone will hate you. You'll need "Grand Army" for you and Prussia be able to fight Austria fairly, so for your next idea I would recommend that. For now I would simply suggest staying HRE emperor and building up a bunch of level 5 and 6 land buildings to get your land forcelimits up to around 300-350, as well as maintaining relations with Prussia and Austria to keep the balance of power in your favour. Trying your best to avoid conflict with Austria and conquering your remaining German cores would be a great idea, as well as attempting to force PU Savoy would be a good idea (inheritance will give insta cores and a lot of northern italy-very valuable provinces). You might also want to war with Sweden/GB to get some Scandinavian/British land and to get some prestige to pull some of Austrian's sphere to you so you can easily conquer some German minors.
Just be ready for an epic war with Austria.
Edit: Just did a mock war with Austria to see the exact value of an Austria alliance at this moment. It is roughly ~230 cavalry units, ~165 infantry units and ~28 artillery units.