I would just work out the dimensions of the room that I'm trying to cool.
Other wise it would be like a mouse shaggin an Elephant?
KWs or BTU loads of calculators to help work that out!
I'm a big fan of American units as is hotter and the compressors they use are Danfoss units or equator rated.
Not cheap but you get what you pay for?
The idea of heat exchange only works when you dump hot air outside so you would want a unit that has a longish plastic funnel that can be fed to a top window.
I'm not holy convienced that opening a top window that feeds the hot air outside is not letting more
hot air inside?

If it was me I would get a hole cut out on the glass and have a cover I could feed the funnel through to maximise the cooling. But the cat flap as I call it would be lockable to stop draughts and cold air in winter catch 22 situation.
Simple machines really just getting the environment right I'm not an expert on domestic units as I custom build for different applications and I have larger units I can make, but I find A/C is not that good for you I prefer climatising in this country!
My car A/C is never on
Simple portable units are just not strong enough and always under powered and eats power like its out of fashion
You say you are bad with heat, but we only had A/C in the last 100 years I'm bad with cold which is ironic as I go down to environments of -55 and where ski clothes in the middle of summer I get funny looks when I suit up
Bottom line cheapest units are ledge mounted where the units are like a box and they get mounted on a ledge where the cooling comes in and hot air is exchanged on the other side of the glass air tight and compact! But are you willing to knock a hole or cut double glazing panel out plus build a concrete ledge for it to sit on?
Manufactures that are good
LG
Daikin
Toshiba
Fujistu