I bought a cheap microphone (Samson Go Mic) for recording the voiceover and a couple of foley sounds. Got really impressed with the quality I got out of it. Just plugged it into my Macbook and started recording. I made sure if was as quiet as possible when recordning and what the sound didn't bounce anywhere (it's always easier to add echo than removing it).

Not sure I understand your problem. By close-up you mean recoding quiter sounds? Lets say you want a sound of dropping a toothpick on the ground. Since the sound is so low you have to crank up the sensitivity on the mic but at the same time you get a lot of noise. In that case removing audio noise shouldn't be any trouble at all.

I have never had a issue like that. Nowdays the sound editing software are so good that you can remove most noise later. Here's a good tutorial about dealing with noise. https://www.youtube.com/watch?v=gZjlS0tD-Wg

While recording the voiceover for 'Exordium' I got some noise. Just followed the tutorial above and noise was nowhere to be found. The problem I faced was that the mouth makes a lot of weird noises (like mouth clicking from the saliva every word you pronounce) so I had to remove every single on of these by hand. Had really no idea how to solve that but stumbled on a couple of tutorials on youtube and found something called Spectral Display. That way I could see every single sound in colors and remove the parts that stood out. Took some time but it was sure worth a clean dialogue.

Have you thought about recording on set as reference and then recording the dialogue later? Most Hollywood movie does that, it's called ADR (Automated Dialog Replacement).

Lastly, I've recorded sounds with the mic on my iPhone. The sound is surprisingly good if done in a controlled environment. You clearly don't need the latest and greatest toys to make a film. It's all about using what you have access to and to make the most out of it.