Qualified Joint Venture and solo 401k contribution

[Matthew J.]

I have a full time job 9-5 where I contribute to 401k in full and Traditional IRA around 1,000 due to income limitations

I also have a side job (Sole Prop) where net income will be close to 50K in 2018. I am planning to declare it as Qualified Joint Venture (QJV) where my wife will be a partner. She is a sit home mom and every year we contribute 5,500 in her Traditional IRA

Up until now, I had SEP IRA where I contribute 20% of my business net income but now that I learned about QJV and making my wife partner, I would like to open a solo 401k for her and let her contribute 18,500 plus the company contribution

1) Can she open solo 401k today and contribute the whole 18,500 in lump sum today for 2018 tax purposes?

2) At the same time, can I still contribute to SEP IRA?

3) Can she contribute to Traditional IRA while contributing to solo 401k?