Before you get to far down your planning path make sure you do not end up with a "City code" issue like I did when I first started planning. Could only go 1000 square feet per outbuilding for inside area. The "dumb part" is I can build as many as I like as long as all are spaced enough from each other and meet lot line set backs. (So why not allow the owner to decide "1" bigger or 2 or 3 smaller but not attached. . . .)
Also had a height restriction which I can agree with but should also take into account the lot, in my case the back yard where we built is lower than where the house is so even with 12' side walls of the shed the roof line is lower than the house. (In the end this met my needs but campers can be tall so 10' tall doors might not be enough for future buyers. . .)
The old 24 x 30 shed I replaced only had 1 door, for 20 years I fought moving this and that out of the way to get the other thing out that door! New shed is 31.5 x 32 but has a walk in door, 3 10 by 12 doors and a 8 x 9 to get mowers and alike out the one side. (Also allows for sleds to come in but I have yet to use it for that as I became too lazy to clear enough snow to get them in that side!)
Also consider your roof line, old shed had doorway on the north side and gable ends east and west so all the rain and worse snow and ice fell in front of the one door. You might not be able to do anything about this on your site but in my case I turned the roof so rafters are wider than the building is long just to avoid ice running down the north side of the building. (Keep telling yourself, cost is only once, use is a lifetime) Since I have 4 overhead doors I still have the ice over 2 of the door but only the small overhead door facing east is an issue as I do not have "driveway access" to get a snowblower over there.
Roof overhang is another thing to think of, I got by with 2 feet but really should have been more. Each person has to build for their needs but I was sick of pulling snow off the roof then moving it so it would not have the next "slide" pile up and pushing back on the shed wall. New building allows the snow slides off the roof to land far enough away that is has not piled up to the shed wall. (Yes, I know if we get snow all winter that I never move at some point it will but if we get that much snow it would be worth moving it! The main thing is the main doors I need to use are not an issue anymore)
Cost, that is really up to you! First info I had from name brand "pole shed" company was for $50,000.00 for just building and cement floor no sight work and not insulated or heated. That shut me down for weeks and almost did repairs and maint on the old shed. I then went to a second name brand and was better price but still no site work included. Luckily for my bank account I found out about a builder through my local electrician while getting price to get power installed. I ended up below the first quote with all site work, including new asphalt driveway, fully heated so it really depends on shopping around and deciding what you want. (Again, spend it once, use it a lifetime. . .)
Site work, in my case this was a killer! When I bought the place years back all the slope ran right to the old shed area. The east end of the shed had plenty of fall to keep and summer time water from ever being a issue, if water would have ever "backed up" then whole neighborhoods of homes would have had water over the roof. However, add in some snow and ice to trap water, that old shed was in trouble! New site had over 3 feet of fill added to ensure water was not going to be an issue. (Also meant the old driveway needed to go. . .)
Keep track of all the things you are adding in though, bare bones start numbers increase quick but in my case was just so easy to have this or that "done with" vs going back later.
Good luck and share pics as you go!