Seriously, I think CA has used my wife's spending habits when they modelled it. 
I love micro-managing so I select the option to manage all my settlements (otherwise you need to have a general in each settlement to do so).
I am currently playing HRE, and after a nice start you find yourself in a mess financially. I'm sure you know all this but here are my suggestions (nothing original btw):
- Always focus on your economy, especially at the beginning. Therefore build all the affordable economic buildings (especially ports and roads) right at the beginning. Later as funds allow upgrade them, and select happiness buildings only as needed.
- Max your tax rate so your settlements have @80-85% happiness rating.
- Establish as many trade agreements as possible.
- Probably early just have 1-2 castles with everything else as cities. I prefer to keep my castles close together, and after each having a barracks try to specialize say artillery in one and cavalry in the other (later as funds permit I eventually build both up equally).
- Minimal garrison using militia that have free upkeep for cities and peasant units in castles.
- Keep exploring the map with merchants for better income sources.
- While you should always be building your military infrastructure at your 1-2 castles (maybe @4 once your empire is much larger), try to limit your troop selection to the most affordable units that can compete with your enemies. Use mercenaries as needed and get rid of them if they cost too much to keep.
- If you find yourself low on funds it is because you have too much overhead (i.e., military), so get them moving and expand your empire!
- If you want to keep Catholic factions off your back, always send a Diplomat right to Rome and give the Pope maps and money as often as possible to improve your relations. When it becomes viable request an Alliance with the Papal States and maintain good relations.
Getting back to my HRE campaign, as mentioned you start out in a good position with regards to the number of settlements and troops. The problem is that you are also surrounded by a number of powerful factions, plus your German-based economy is very sluggish.
I attacked Poland and nearly wiped it out (sorry Macca
). But then Venice attacked and later Milan and Hungary. My empire started falling apart, I couldn't access decent troops, but luckily it didn't matter because I had no money anyway. 
Well after turning down Milan's proposal to be their vassal, Denmark attacked and made the same proposal. I accepted and instantly received money, new trade agreements, and was able to restore some previous alliances. Finally my economy started moving forward and I was building up a decent military.
Shortly after that there were two quick elections for pope. My first attempt failed but I was successful at the second. So here's the deal for any new popes out there. If you are lucky you can call a crusade against one of your enemies (or allies
). So given the strength of Milan, I choose one of their cities for a crusade. After a bunch of turns, and with the help of France's crusading army, Milan's military might was destroyed and I gave the city to the Pope as a gift. Btw if you are going to select a city to crusade against make sure it is far away from your empire, or else all these large foreign armies will turn on you after the crusade. Apparently the chaps don't feel like walking back home.
Well anything useful here mate? Sorry I forgot the real important stuff.
TS!
I found Milan, Poland and Venice to be quite a pain in the butt when playing Russia. Think I'm gonna ask my Alchemist to make a stink bomb. That should do the trick! 
I'm surrounded by grumpy old men!
