I recently purchased a 2005 Mazda 3 hatchback with the 2.3 175k miles for $700.

I was told it needed a clutch, so I bought a clutch kit, master cylinder and slave cylinder and had my mechanic install everything. 

When I have the clutch pedal to the floor and I put it in 1st gear, it grinds, but if I wait a few seconds, it doesn't grind. Same when I put it in 2nd gear, it will grind unless I wait for the rpm drops to about 1.5

Also, the car is a pain in the ass to start. With the clutch pedal down, it doesn't start, I have to push on the clutch with excessive force until it will want to start. I tried replacing the clutch safety switch and I couldn't get it to start at all, so I put the old one back in. 

I don't have if my mechanic did something wrong or perhaps on the parts he installed isn't working correctly.

He's ase certified and has always done good work on all my vehicles.