Just have fun with it. Upgrades are whatever but I went with Health/Attack and eventually defense. oh and armor weight.
The layout of the castle is important too cuz I think it scales enemies differently. You pretty much wanna go main castle, then right to the forest, up to the maya (tower?) and then down til the darkness. The levels are randomly generated unless you 'lock' it but they are always same direction (unless dyslexic, lol). If you do get to a boss and you feel you can beat it, just keep locking the level (with the architect) and you can keep using the portal to retry.
This game reminds me alot of demons' souls and dragon's crown with the new game + and retrying the bosses and incremental improvements. Good Stuff
I texted TehCro 2 nights ago when I started the game and told him I just keep dieing, lol. He had already beaten 2 bosses at that point

I was busy trying to make $ with cam chix. Rogue Legacy Plat > Cam Chix. My fail.