You can get all the patches from the TaleWorlds official website. Just select your game and go to the download section, and it will be here, either in patch or directly download the latest version.
Note that 1.54 should only bring modifications relative to NW, and the mod should work under 1.53 if if doesn't use any NW specific content, So the latest real Warband native version is 1.53, that you already have.
I suggest you build an army of Saranid Mamlukes. They are excellent detergents towards Kahnid Horse Archers, because of their extreme resilience and armored horses. Make up for the lack of ranged units with some horse archers of your own though. Once you have about 20 mamlukes, the Sarranid melee horsemen, (gonna take some time, but given that Swadia's gone (they're always first to kick the bucket) and you're cutting into Vaegir and Sarranid territory, 20 should do it), defect and try to conquer their southern-most castle (forgotten its name). This castle is in a narrow passage, and should make it easy enough to defend or flee from if necessary. Be careful when assaulting the castle though, as the Kahnid are very archer-oriented, making the ascent on top of the castle walls a rather interesting experience...
Get some lords on your side, preferably Kahnid, to support your cause, and make a stand at the castle should the Kahnid come at you in numbers.
It would be advisable to capture said castle after the majority of the Kahnid noyans and their Khan have just recently fought a major battle, and are low on troops.
Well, that's how I'd handle the situation. It's never too late to satiate your desire for World Domination in M&B:W. Ever.
Best Answer
You can earn a lot of money by finding tournaments and entering them. The tournament reward is usually not too great, but its possible to earn a few thousand denars by betting on yourself. If you place a max bet on yourself each round, you can earn up to 4000.
To find tournaments, go to a city and ask the arena master if there are any.