Annapurna Base Camp trek is regarded as a moderate trekking trail in Nepal. With many accents and descents along the trail you need to have some experience of walking for a few hours (5-7 hrs) per day. The trail after MBC is gradual although the altitude will make it difficult for some hikers.
We suggest you hit the gym for a few weeks before the start of your trek or walk for a few hours. General exercises prior to your trip will be beneficial for the trek.
Yes, it's a great choice for a first multi-day trek with proper preparation.