What should i do first?

I would start general with the amount you want to and are willing to spend, the colors, the general “feel” (romantic/rustic/themed) and go from there. Pinterest is a great help with just getting your ideas sorted. Then move through with whatever you’re excited about most (mine was my dress!)

You need to start booking vendors, find outfits and work on save the dates.

I would book vendors first that book early- photography, catering, florist, DJ

Budget first.
Guest list, colors/theme, officiant, dj, photographer, caterer, florist, bakery, hotel block, dress, wedding party, their attire, groom attire, decorations, signage..whatever else you decide to have.

I'm going to assume you already have your budget, rough guest list, and "feel" that you want taken care of. If not, start there. Otherwise, decide which vendor is most important to you. For me, it was photography, so I looked for and booked my photographer as soon as I had our venue booked. Assuming July 2020 is correct for your wedding, you're going to want to lock in those "big" vendors sooner rather than later. Think photographer, caterer, DJ, florist, officiant. The WW vendor tab has lots of fantastic vendors in your area that can help you narrow down your choices.

Venue is a great thing to start with. I'd focus on overall budget & guest list. Then focus on the main vendors (photography, catering, dress, DJ, officiant).