It's a bit more complicated than that. As @BMK indicated, you have to depreciate the improvements (but can't depreciate the land portion) generally under a 30 year straight line schedule. So the principal part of your mortgage isn't deductible in the way you think. The HOA fees, insurance, and interest may be deductible directly (or 25% in your example), the property tax may fall under SALT limits you're already going to hit in that example since you're talking about a passthrough. So something like $750/month * marginal rate of 39.35%=$295/month in tax savings.Yeah, keeping it simple, if I can buy a $1M condo in Miami it would be like $3500/month in principal/interest, $1400 in property taxes, $400 per month in insurance, $1200 month in HOA fees. Let's say 1/4th of it I use as my home office. I don't know what percent is the principal first year, 30%? So if my logic is correct for a home office I would get to deduct 25% of the 250k above the 750k I can deduct interest, property tax, HOA, and insurance fees? So like (3500)(.25)(.25)+(.25)(1400+400+1200)=968.75 plus 25% of the mortgage on the first 75% of the $3500 which will be like 30% principal the first year. So like 196.88. So that'll be like $14k per year extra I can deduct. By deducting 14k off my income for my home office I only save 39.35% of it which is about $5500. Still not enough to pay for even the 1.45% in Medicare my employer has to keep paying. I think I'll stay W2.
BTW, it seems damn expensive to live in Florida! My property tax would be $875/month on a condo of that value, my insurance would be $200/month, and since I live in a house no HOA.....and I'm in what the Florida folks consider an "expensive" blue state in the mid-atlantic.