Also, I am passionate about communal living so I would love to have at least one property that I hold onto and live in and establish a more intimate community around shared meals and other activities.As San Diego is such a competitive market right now, I'm researching other markets I can invest in.

I would keep doing whatever your doing to save 250k in cash by the time your twenty five... keep doing that forget real estate.. only way you pocket big money quickly in real estate is either in the rental business you start with big money.or you do value add.. flips new construction  land rezones ... etc etc.if your looking to do it land-lording.. then that's a slow boat.. and of course you have plenty of time.but the way to scale in rental is to pay cash then value add so you can hopefully refi all your cash out then do it again.this is communally called BRRRR  although some think this BRRR is new its actually the way most investors did things prior to the GFC  when you were the rip old age of 15..

If you are having to share communal space. 

To me, if you're going to have to come out of pocket to replace the roofs, resurface the parking area, replace big communal boilers, etc. in 1-2 years you might as well add (for analysis) those into the purchase price as your cash-flow won't build reserves fast enough to cover those.

You can be a strict or as loose as you communally agree too - and with a certain level of agreeance (usually 67%) the rules can even be changed from time to time. 

the vehicle should be parked in a non communal part of the community namely a garage.The hoa has the right to enforce its rules 

I actually walked the property today, and in one unit the third "bedroom" was a glorified pantry without a closet, and the laundry room was communal with the top floor tenants having to go outside to access the door leading to it.

Utilities & Lawn/Landscaping: This might not apply to a duplex by when you hit 4 units don't be surprised if you (the owner) are paying water for the whole building, you may have a dumpster fee, if the lawn is communal you're likely paying to keep that up.

You might also try something that will bring your community together instead of making it raffle competition - for example, setting a community goal amongst your tenants (reaching a certain number of A's B's and C's, a certain number of units taken/completed, etc) and then creating a communal reward when the goal is reached, such as a big BBQ where people can invite their friends/family and the tenants get mentioned/honored.

They are usually more communal in nature and if that works for your perspective, great.