Extract Reads by region from a BAM file

Question

Hi I want to do two things.

1. Extract number of A bases from my BAM file with >= 20 reads aligned.
2. and I want to do that by genomic region. i.e. I also want to know if the particular A falls in 3'UTR, exon, intron etc.

Is there any tool for that? Can I do it using samtools? please help

I tried using smatools for extracting aligned A bases and I used samtools view awk function for that but that gives you the number of all Aligned As to reference genome not the As with >= 20 reads and also no region information.