The C4 Mak is pretty heavy, so get a good mount that can take it, and any upgrade you decide to get. The Star Adventurer GTi cannot effectively handle the C4M.
The 4SE is pretty difficult to image with, F/13.25 focal ratio means you are going to need very long or a lot of exposures to get images with good SNR. I used mine from a balcony for years to some success, but found it more capable as a for-travel visual only scope.
AM3 is a good mount, but with the payload capacity of it, you might find yourself limited in higher aperture options after the 4SE is retired.
A new or used HEQ5 or EQ6R can be found for a little under or over $1000 USD these days, so if you are interested in saving for a while to get a mount that can handle pretty much anything you throw at it, they are outstanding.
Alternatively, if you want to keep it even lighter- featherweight- iOptron’s lighter GEM28 and CEM26 are superb for the size of the 4SE, but you’ll find it’s capacity inept for any upgrade that isn’t a smaller APO or lightweight newtonian (~6”).