Unless there is a history of allergies in your family, you don't need to stagger the foods you introduce. They can eat anything you would normally eat, minus honey, whole nuts and sugar/salt from 6 months. I wouldn't necessarily worry about a reaction. If you get one, it will be obvious (we have a possible allergy and it was pretty obvious what caused it even though she eats everything). We started lunch at 6 months and worked up to 3 meals by about 7.5 months. You can really do it at whatever speed works for you and your baby. There is no rule that they have to be eating so much by a certain point. I just found that worked for us. She didn't eat that much at first anyway and it took me some time to get up to speed with planning meals for all of us. But I'd move in the direction soon of offering for meals what you would normally eat yourself, whether as finger foods or mashed. So for dinner, we were doing cheesy jacket potatoes, roast veg, pieces of roast chicken, baked fish, plus sometimes things like rice cakes and toast with various things on it (avocado, cashew butter, mashed banana, hummus, etc.). That way you can introduce more protein, dairy, and grains in addition to fruit and veg.
As for a sippy, I'd offer one by putting a sippy of water on the tray when you're having a meal. He may not pick it up for a long time, but it will at least get him used to it. My daughter didn't really drink out of it until about 9 months, but she was getting plenty of milk so she didn't need the extra hydration. Giving it to her to play with in the bath (or outside when it's warm) helped because she could dump it upside down and shake it and play with it and not make too much of a mess while she figured out how it worked. You shouldn't really offer juice. It's too sugary for them. I think they say at least not before 2, but ideally not for awhile after that. All they really need is water. They should get their calories from food and milk. And it saves you spending money on something extra since water is largely free.