What you need to be able to invite a random courtier is for them to be at least -1 with their liege (preferably more), and at least 50+ with you. The actual number you must hit are roughly their opinion of you - 75 (no reason to move, base reluctance for all diplomacy, other) > their opinion of liege. It is ridiculously difficult early on to invite someone who hates their liege and loves you and have them accept, and it is one of my pet peeves with this game. Later on the 'unable to press my claims' modifier will make it a ton easier to find people to invite but right now you are out of luck.
If you have decent diplomacy use some of that blood money to gift them but only if you're sure it will tip them since your income is probably horrendous despite having a bit of cash. Hopefully you can come out of it with at least a 15+ in whatever stat, going straight down the list. If they're positive at all with their liege don't even bother looking whether they'll come as they won't. Hopefully you
quickly find that charitable great steward with the cruel greedy arbitrary liege rather quickly, but be warned this will be tedious.
== Day 2-20 ==