@Shane Craig
1. It will take longer, on average, to lease a commercial space. Typically 6-9 months is what I advise clients, it can happen sooner or longer, but this is a good rule of thumb. I am going to elaborate on the tenants in the next answer
2. I HIGHLY recommend meeting with an attorney and have them draft a "base lease" document that you can "plug & play" with all of your tenants. You need a lease that is tailored to your comfort level as an owner, as well as one that is in line with the financial goals you have for the property. With multiple types of leases available in commercial, you need to make sure that the lease you are using for your tenants is doing what you thought it would do when you did your underwriting on the property.
Commercial tenants can be great, but not always. If you are providing any extra buildout as an incentive to get a longer term lease, I'd recommend having the prospective tenant sign a "personal guarantee" for a minimum amount of the unamortized Tenant Improvement expenses that you provided as the incentive to get them into your building. They can be great tenants, if you find the right one you'll have them as a tenant for a long time, but on the flip side they can be just as bad as the horror stories you hear about residential tenants. Building a good relationship with your tenant goes a long way.
3. I've seen success with "loft style" apartments. Use a split-system HVAC unit that hangs on the wall to handle all the heating & cooling, it's very cost effective and they work great for open layouts, you can hide these easily. (Would also recommend these for the commercial space downstairs and the garage...can cut out on putting in full on HVAC units.
Don't out kick your coverage (competition) when it comes to the finishes. Spend $ to make it look nice, don't go the cheap route, but also don't over extend yourself here and stick to your budget. If you start seeing that you have to go above budget to make the space rentable...then that's either not the best use of the space, or the property just isn't right for you
4. Look and see if it is eligible for historic tax credits at the State or Federal level...they offer incentives for rehabilitating certain older properties
5. Study the market, find out what is working and what isn't. Don't try to reinvent the wheel, commercial is simple as long as you don't try to take shortcuts or overthink.
"If you were a tenant looking for new space...what would you want?" - Put yourself in their shoes so you understand both sides. Hope this was helpful