Is this brush smoothing?

Yes since it cuts down drying time significantly.

Is this brush good for fine hair and is it soft on the scalp?

Yes this brush will work will to brush fine hair and it is gentle on the scalp. If your hair doesn't tangle easily, then you can also use it for detangling. However, if it does tangle easily, then you will also want to get a brush specifically for detangling such as: https://www.amazon.com/Olivia-Garden-iDetangle-Brush-Fine/dp/B071DVHVVH?ref_=ast_sto_dp&th=1&psc=1 https://www.amazon.com/Olivia-Garden-Detangler-Fine-Medium-thickness/dp/B07TLP1856?ref_=ast_sto_dp&th=1&psc=1 Happy styling! ~ Olivia Garden

Is there a way to clean the build up on the bristles near the base?

Thank you for your inquiry! We hope that you are enjoying your brush. We highly recommend our brush cleaner, it is amazing to clean all your brushes (any brand, any model): https://www.amazon.com/Olivia-Garden-Cleaner-Individual-Pieces/dp/B00ABTJAJM/ref=sr_1_3?dchild=1&m=A25WZCI7CCJL9A&marketplaceID=ATVPDKIKX0DER&qid=1573260952&s=merchant-items&sr=1-3