Cards, posters, t-shirts… There’s no “do-it-all” type of print device out there.
I’ve been in production print for 13 years. There’s a reason we have 6 print devices. Each machine produces it’s unique specialty. Two sheet fed digital devices (your cards, flyers, etc) - Two wide formats (Architectural and posters/banners) A 5 color laser printer for heat transfer sheets, And a sublimation machine for promo items (mugs, bottles, pens etc)
Now, I can say, you can pick up an inexpensive heat transfer press (t-shirts) for a couple hundred dollars (US) and a color laser printer for an additional $150-200, and a pack of self weeding transfer sheets for 50-75 bucks.
Find a laser printer that can also do 100# Cover (275gsm) and up, and this could also double as your card printer. However, you’ll have to find a way to accurately cut your printed items (one that doesn’t take you all day to do so)
Posters… could be tough - Wide format printers aren’t too expensive as far as print equipment goes. You could walk away with a near professional quality wide format for a few thousand dollars. I think Epson makes a few mini-sized ones that could maybe to an 18x24in poster in the thousand dollar range.