The contribution limits for 2018 are $5,500 per year for those under the age of 50. If you are 50 and older, you can contribute an additional $1,000 per year in catch-up contributions, for a total of $6,500 per year.
The 2019 contribution limits have been increased to $6,000. Catch-up contributions for those over 50 can contribute an extra $1,000 for a total of $7,000 per year.
Future years' contribution limits are subject to change on irs.gov
Yes, but your contributions are aggregated. You can still only contribute up to the 2019 limit after adding your contributions together. For example, $3,000 to a Traditional IRA and $3,000 to a Roth IRA would max out your 2018 contributions to IRAs of $600.
It does not matter if your spouse contributes. You can both contribute the full amount for which you qualify to an IRA.
You can contribute to a normal 401(k) and a (Traditional or Roth) IRA. Be sure to report your modified adjusted gross income correctly.