Q1: Did you mean 8843 instead of 8848?

You can claim 5K tax treaty coz even you are resident for tax purposes, you still qualify. See Article 20,plz.

Q2: You have to pay tax for interests coz you are resident instead of NR now

But I guess this is the trade off, you gain alot from Std. Deduction. NR do not have S.D?(plz correct me) And MFJ has lower tax rate than MFS in which NRs have to fill that way.