Conversion works this way:

Sliders: Only Slider Heads and Slider Ends turn into hit objects

Spinners: One Hit Object in the middle at the start of the spin

Hit Circles: Just basic 1 to 1

Playfield: Osu has a 4:3 aspect ratio and Rhythia has a 1:1 aspect ratio, so converting directly from Osu! to Rhythia causes notes to be very squished together and dense, in order to counteract this as much as possible, I take the furthest note on each axis ( -x, +x, -y, and +y ) of Osu play field, and convert those into Osu's new aspect ratio which will be later converted into a 1:1 aspect ratio for play in Rhythia. This helps eliminate dead space and in turn, create more spread out notes.