1. Theoretically, you're right. When all subcarriers are modulated the (baseband) bandwidth of an OFDM signal is approximately $f_\mathrm{s}/2$. An ideal rectangular filter before A/D conversion would be needed at the receiver to avoid anti-aliasing. As such a filter cannot be implemented in practice, some subcarriers remain unmodulated to make the OFDM spectrum narrower. This zero padding in frequency domain corresponds to oversampling in time domain.
2. An OFDM symbol including guard interval consists of $N_\mathrm{c} + N_\mathrm{G}$ samples each of which has duration $1/f_\mathrm{s}$. The "oversamplingrate" parameter in your formula is not clear to me. As a rate usually has the unit 1/second your formula's result is without unit which is a contradiction to the left hand side of your equation. Any reference for this formula?

1. Theoretically, you're right. When all subcarriers are modulated the (baseband) bandwidth of an OFDM signal is approximately $f_\mathrm{s}/2$, where $f_\mathrm{s}$ is the sampling rate. An ideal rectangular filter before A/D conversion would be needed at the receiver to avoid anti-aliasing. As such a filter cannot be implemented in practice, some subcarriers remain unmodulated to make the OFDM spectrum narrower. This zero padding in frequency domain corresponds to oversampling in time domain.
2. An OFDM symbol including guard interval consists of $N_\mathrm{c} + N_\mathrm{G}$ samples each of which has duration $1/f_\mathrm{s}$, where $N_\mathrm{c}$ is the number of subcarriers (equal to IDFT length) and $N_\mathrm{G}$ is the number of guard interval samples. The "oversamplingrate" parameter in the source you referenced seems to be some additional oversampling factor of the transmit signal. What it's needed for, I don't know, because I don't know this software project.

Regarding the terminology of symbols: in OFDM each subcarrier is modulated by a complex value. All subcarriers keep their values during the duration of the OFDM symbol. Sometimes these values are also called symbols because they're usually taken from an QAM alphabet. A subcarrier cannot contain several symbols at a time. To sum it up:

• symbol: Value of a subcarrier
• OFDM symbol (in time domain): entity of all time domain samples that are obtained by taking the IDFT of all subcarriers plus the guard interval.

The OFDM symbol rate is therefore given by

$$ R_\mathrm{s} = \frac{f_\mathrm{s}}{N_\mathrm{c} + N_\mathrm{G}} $$

Note that the number of zero padded subcarriers is irrelevant for the calculation of $R_\mathrm{s}$.