For APT if you have a good line of sight and decent antenna you really, really don’t need an LNA. For LRPT: maybe. With overhead passes from about 60-90 degrees you shouldn’t need one. The signal has a lower power density because of the wider bandwidth and similar power to APT. Overhead passes should give you an SNR of around 10-15 dB and up with an RTL-SDR dongle, which should easily be enough for demodulation. For lower passes you may find you lose data and sync occasionally unless you have a decent LOS and a well-tuned/aimed antenna.

If you move away from VHF to higher bandwidth/frequency signals later on then you’ll definitely need to look into one, (as well as bandpass filters appropriate for the band) and don’t forget they’ll need power (through whatever method required). Check the current draw and that your power method or SDR can actually provide enough.

These can be useful, particularly if you are plagued by intermod on your SDR. LRPT works best with a decent amount of gain, so by suppressing those signals out-of-band you’ll get less issues when you turn it up. You can buy some that work between 136-138 MHz or build your own if you’re savvy. Also useful if you have other RFI in the area and can’t operate from the middle of a big empty field. Just check the specs first and make sure they do what you need.

This also applies to those weaker signals at lower angles (for both APT and LRPT). Sometimes you’ll want the gain up to help and that lets the intermod in. Filtering before gaining up will mean your radios front end won’t have as many issues with other signals interfering.