1) What are the best ways to increase my imperial authority? I have already broken some nations free, added lands to the HRE, but cannot seem to come up with anything else. Should I just keep attacking HRE members to break nations free from them?
These are the best ways, especially releasing HRE states (which you can exploit a bit by annexing some yourself in order to re-release them). The more HRE states there are, the better the bonuses you get, and small states are easily cowed into passing reforms. You can also defend HRE states against outsiders (although few powers will even try once you are strong). Adding territory is good, but it can be a limited resource, so you may want to save some of your lands for the later decisions.
If you take over as Emperor during the Reformation, you can also get a boost by imposing your religion on the HRE member states. You can be fairly indiscriminate with it as a Catholic, but both the rewards and risks are greater for a non-Catholic emperor.
Annexing electors in order to appoint new ones can also be fun, but there are limited opportunities to do it.
The first potentially awkward reform for you (if you are also an HRE member) is Ewiger Landfriede, as it prevents you from waging war to break up the HRE states into smaller pieces and hurts your army tradition, although as a slight plus, it ensures you will routinely get the 'peace within the empire' modifier, which generates a steady income of IA. The real power play as Emperor starts with Erbkaisertum. At this point you can forget about elections and eligibility, so if you have vassalised electors, you're free to annex them if you like. The real boon though is that HRE vassals don't consume a diplo slot, so you can immediately start diplo-vassalising indiscriminately. You can finish the job later with Revoke the Privilegia, but it's best not to rush this one as ideally you want it to be unanimously approved. Finally there's Renovatio Imperii, which is a double-edged sword: on the plus side you annex everyone left in the HRE and form a Germanic cultural union (if your primary culture is Germanic), but on the minus side you become just another country and lose all your special bonuses and powers (including the ability to have hordes of vassals without using up diplo slots), as well as killing off your country's special historical events. I'd say Renovatio is usually not worth it if you have major expansionist ambitions, but it works out well enough if you are Germanic and just want to unify you culture group ASAP.
