If you're not familiar, with the merger they enacted some rules for who is eligible for certain cards now. In general if you have (or had) a SPG card it prevents you from getting a Marriott card and vice versa. I think this blog post is helpful in seeing what you can get based on your history -
https://frequentmiler.boardingarea.com/navigating-marriotts-byzantine-credit-card-rules/
Also with the merger is the change in points needed for the Swolphin properties. Standard redemption is 50k per night now, and starting next year Marriott will enact peak and off peak pricing so a night can be between 40-60k points. (new award chart can be seen here:
https://members.marriott.com/marriottrewards/). So the sign up bonuses on the cards won't go as far now. There's also a Marriott Village not far from the parks that are all Cat 4s, so only need 20-30k per night for those.
Outside of Marriott points you could look at other travel points that can either transfer or be used to offset a cash booking. Both AmEx MR points and Chase UR points transfer into Marriott, but it's not always the best value for those points as Marriott points are worth less than 1 cpp (Marriott values them at .9, I think most people value them around .7). Depending on when you go you may be able to get a discounted cash rate that may work out better.
Otherwise, spend spend spend on the cards, stay at Marriott/SPG properties anytime you can, and look for partner earnings or promotions to augment any sign up bonuses you might get.

Chase and AmEx were offering upgrade bonuses on existing cards and AmEx introduced a new SPG card you could try for (higher annual fee though as it's a luxury card).