The wall space clearance requirement of 30" is from the floor to ceiling. And the panel does NOT have to be centered. Unless you have like a 6' ceiling or a lot of things like counter tops in the way etc, I don't see why this would be a problem.
The process of upgrading from 100A to 200A is not just a swap of your panel. It's a little complex and most definitely has to be permitted. It is doable yourself. In any case, it's good to understand the steps whether you do it yourself or hire an electrician:
Check with the utility company to see if your "drop" (wire form the pole to the house) is capable of 200A. Normally, a utility company will have to upgrade this themselves. But sometimes you'll have to pay.
If you have a separate meter box with main breaker and the separate panel in the house, the line between the two will likely need to be upgraded to 200A line.
You will need a 200A new panel in the house and all new breakers that are up to code.
You will need a new meter box and 200A compliant meter from the power company.
You will likely have to upgraded / bring other things into compliance to pass inspection. Such as, the ground wires. Many areas require you ground to your main water supply coming thru the foundation along with the two grounding rods. You may need to install special breakers if your bathrooms aren't GFI'd for those circuits.
Basically, you'll have to pull the permits. Have the power company pull the meter which will shut off the power. Install all the new equipment with the power off and then get it inspected. In my area of the country you can get what's called an "open circuit permit." Basically, you can hotwire your new 200A meter box so that you can get your power back on while you wait for an inspection and for the power company to install the new meter (they generally won't install it until you've passed inspection). This just means you're running power for a while with no meter and being charged an "average" rate.
I am pretty handy and wouldn't tackle this myself. Though, there are some good youtube walkthrus and it can be done. If you price it out, keep in mind the prices will vary wildly. I had my house done for $3000 and that included eliminated a remote panel in my basement and a few other upgrades aside from the 100A > 200A change. But, i got several other quotes and they were: $4800, $12000 and $6700. Like I said, get lots of quotes! Figure on at least $3000.