I think you're right Blue in regards to centre midfield - although having both Bowyer and Faye in the squad but playing one to stabilise and protect the defence might be a good idea. I hear two clubs have bid £750k for Jack Cork and he would be ideal to partner one of them. Likewise a centre-back signing would add competition but Gerrard and Hudson together are more than good enough to get yourselves out of the league. We've benefitted with Tate (as unpopular as he is with you guys) because of his willingness to play all over the park without grumbling and more often than not playing well. He's so useful for cover and makes the squad more flexible - so maybe the 3rd centre back should be a lad who can play full back/defensive midfield too...
I know what you mean about players returning but when Earnshaw came on against us in the semi he looked sharp (good goal) and it would be nice for the club to have two strikers who are 100% Cardiff. You would know that a defeat would hurt them - which was maybe questionable with one or two (certainly not all) of the loan signings last year. You would lack height upfront with them on but there's no reason not to keep Parkin on the bench if you want to mix things up - although Ellington is more mobile (as is my flat). I know what you mean with King, CityAce – sometimes the baggage is too much and the reputation of the player can dent that of the club.
Other than that a couple of young lads fished from overstocked Prem youth teams might be determined to make their mark - but would be better if (like Jack Cork) they were available as a permanent signing. Having said that, your youth academy has been quite productive in the past and, no doubt, you'll have a few effective players, home grown and dying to make their mark, just waiting to be given a chance. A few sensible experienced heads (maybe not King then! - although Bowyer seems to have sorted himself out... Danny Murphy is on a free - would he be willing to step down a league?... again that problem of age... But you could seek out players who have experience of captaining teams or of promotion - people who can steady the ship with a word or by example).
It's a difficult balance to strike - too many old players and youngsters skin them and they get knackered in the run in, too few and the ability to protect a lead or beat a few wobbles suffers.
Managerwise I know what you mean with Bellamy. Cardiff is an ambitious club and a tough one to come into and settle what would be a significantly different first eleven. However, stepping down from Man City and letting go of a lot of salary would buy time in the eyes of the fans/media - it would be one of their own doing it for the right reasons. Maybe a seasoned assistant manager alongside him with impeccable coaching credentials to be his Brian Kidd. I think goodwill would certainly relieve some of the pressure on the team and allow them to fulfill their potential.