It can get pretty frustrating! Everyone goes through this once an eye for details starts to develop. I do like your composition, so it's just the technical details that need some tweaking.

For slide film, I'd start with Fuji Provia. Although Velvia is often recommended, it is an extremly difficult slide file to deal with. Provia will serve you better. With slide film, you will have to be very careful about exposure: it doesn't have the exposure "forgiveness" that print film has.

Some Ilford and Kodak B&W is meant to be developed in C-41 (color print chemicals). Other B&W films use traditional B&W chemicals. I'm not into B&W so I'll leave recommendations to others. In all cases, a low ISO will give you lots less grain than higher ones.

You can get pretty good deals on a film scanner these days. With digital photography taking over and scanner technology improving, the prices have come down. I have a Canon 4000 that is an excellent bargain. It's slower than the equivalent Nikon but the quality is just as good and it's less than half the price. For that amount of cost difference, I can be patient!