Put one point in each manor upgrade, to unlock additional upgrades, and no more unless you know what you're doing. Runes and equipment are cheaper and more flexible than the base upgrades, since you can tailor your loadout for each life.
Two sprint runes and one fly rune should be enough to get you through the game and clear most of the fairy chest challenges. The rest I put in vampirism, but there are probably other viable options. Gear-wise I'm using mostly blood armor, it's very heavy and reduces your HP, but I'm up to 10HP per kill right now, which is crazy.
My thoughts, speculations, etc.
Paladin sucks. Nothing special, and the shield will just drain your mana. I guess equipping siphon runes could help but bleh.
Barbarian I'm not so sure about. Not that strong but shout pops projectiles which can get you through a couple fairy chest challenges, and with all my vamp runes I'm practically unkillable.
Archmage with Dextrocardia seems pretty awesome, you basically end up a barbarian with a much more useful ability and free siphon which covers for the smaller mana pool.
Assassin sucks.
Shinobi's awesome. Huge damage, crazy mobility, probably my favorite class.
Miner is good for getting lots of money and since the combat's mostly skill-based it's pretty good despite its weakness.
I'm not sold on Spellsword but he seems pretty decent.
Not a fan of the lich but I'll try that crowstorm guy when I get a chance.
There's one more class but it's very far up the manor and costs 5000 gold. I'm not going to spoil anything but it's the opposite of worstiality.
I think I've finished the diary pages, and it sounds like your reward is going to be some kind of Monkey's Paw thing. The Prince, who would inherit the kingdom if he brought back a cure for the king's wounds, found the fountain of youth. King's cured, but he'll never inherit. I'm guessing whatever I get is going to be similarly unwelcome.