Not even close
Look at how service panels work. There are actually two Poles, L1 and L2. Since you are dealing in 120V loads, you can pull 200A off each of them.
A 240V load like a house air conditioner pulls off both at once. You have none, however.
Aside from the 120V issue, you are supposed to radically oversubscribe panels. A family will use the power a family wants to use, how the circuits are subdivided will not affect demand.
The purpose of breakers is to protect wiring. If you subdivide a circuit, say, into 3 circuits, each set of wiring needs its own circuit protector (breaker). That's all that is. And Codes have required a lot of circuit division of late, which is why each bathroom and bedroom requires its own circuit and you are putting 6 circuits in a kitchen.
Tom rewired his kitchen from three 15A circuits to twenty 20A circuits, even provided 2 separate circuits on each countertop receptacle. From the panel it looks like a leap from 45A to 400A, but Tom's wife doesn't know that. She might raise her usage from 30A to 40A as she learns not to be skittish about breaker trips, but that's all.
A lot of your general-use circuits are dedicated circuits with almost no load on them. Fridge, gas range, gas furnace, gas water heater, lighting circuits... These might draw an amp or two yet you are figuring 15-20A for each. This is just the nature of satisfying modern codes, which do a lot of subdividing circuits that would've been combined before. A lot of European homes have 6 breakers.
One thing we do not oversubscribe is big 240V loads that are likely to be on at the same time (i.e. Not electric heat and A/C).
Another type we do not oversubscribe is loads we plan to run 24x7, e.g. A Bitcoin miner will buy a house and (if he listens to me) will spread the servers around the house so the existing 30A A/C can cool it. If he is putting twenty 10A servers around the house, he has to make sure they are balanced 10 on each pole, and provision a full 100A for them, plus the 30A A/C.
In other words we think about the loads that are likely to be on at once, worst case, and fudge in a safety factor.
Make it legal
This studio subdivision, are these mancave/art studio, or do you even have the sparkle in your eye of renting these units out? If the latter, get to the city permit agency and have a lengthy talk about subdivision - if it is legally possible and what utility divisions are required to do it. For instance you will need separate panels for the studios, because the tenant must be able to reset his own breakers without having to call you. And they may need to be (or be easily rearranged into) main panels with their own meter. That's code saying that, not my opinion.
My opinion is, existing units often have these ganky arrangements where a tenant has to call maintenance to reset a breaker, or get into tense fights with landlords over excessive use. Those are terrible which is why they've been written out of most codes today. Just last week we had a landlord in here who evicted her tenant due to excessive electricity use, then admitted the electricity use did not drop after the tenant left, and said "surely it can't be my ________" which it most certainly was. The landlord was a complete ____ obviously, but the landlording business turns people into that. Good meters make good tenants.
And now is the time to be fitting that stuff, it will be much harder later. Aside from the obvious, once the units become rental units, the work must be done by a licensed professional. The moment of it becoming a rental unit is an important detail that defines how much you can DIY.
Best Answer
My gut feeling is you'll be OK for some amount of EV charging, but not necessarily 60A. You need to do a formal Load Calculation. Since you are going to get an electrician anyway, one option is to assume that you will be able to spare at least 20A for EV charging, and move forward anyway. EVSE (a.k.a., the charger) such as a Tesla Wall Connnector is identical for any range from 20A to 60A, sometimes even higher. The decision of how much power to provision for EVSE only affects two things - how it is configured (switches or some software setting) and the wire size needed.
Load Calculation
As you already know, it is not add up the breakers. And actually if it was add up the breakers, you would not necessarily be in such bad shape, because you have 200A @ 240V but many of your breakers are single breakers at 120V. But that still isn't the way to do it.
So how is it done? By a combination of:
It gets complicated. But the end result is a single magic number that incorporates typical usage patterns. You subtract that number from your service (200A) and see what is left.
There are some online Load Calculation web pages as well as many printable worksheets and some Excel spreadsheets. Or your electrician can do it (my electrician did one as part of a heavy-up - there was no question about whether I would be OK in 200A, but it had to be done as part of the process).
How Much Do You Need?
For most people, most of the time, 20A to 30A is plenty. Most people are able charge their EV overnight. Most people drive 100 miles or less per day. 8 to 10 hours at 20A is enough to add 100 miles (typical) of range. So if your Load Calculation only allows for 20A (I think you'll be able to do more in this particular case) then it just doesn't matter. You set it up for that and everything will be just fine.
If your Load Calculation allows for 40A, then you have to consider whether to use the full amount available or not. There are two issues:
20A uses 12 AWG wire (standard for lots of circuits). 30A uses 10 AWG wire (standard for clothes dryers, water heaters, a lot of ovens, etc.). 40A needs 8 AWG cable or wire. 50A needs 6 AWG cable or 8 AWG wire. 60A needs 4 AWG cable or 6 AWG wire. Unlike some things, most EVSE requires copper wire (aluminum is much cheaper at large sizes, even though it usually needs a size larger than copper for the same circuit). If it is 20 feet then no big deal. If it is 80 feet then it starts to add up. Not a huge deal, but something to consider.
If you have a Load Calculation of 100A and use 60A for EV charging then you still have 40A for future use. But if you have a Load Calculation of 150A and use all of the remaining 50A for EV charging then you will have a problem if you ever want to add something else - e.g., larger HVAC or larger oven. You would then need to look at either load shedding options (effective but can get expensive to retrofit) or end up reconfiguring the EVSE for a lower maximum charge rate (easy on some, nearly impossible on others).