I think you will be short
Assuming you don't want to target the "affordable" spa market, it will probably take considerably more than 100K to make a go of it.
A 3-star spa facility costs $50 - $70 per sq ft for build-out / renovation / decor / furnishings. 4 star is up to $100 / ft. This depends on how much of the existing space is usable as is, or with just a decorator's touch. Equipment would probably be extra. A wet treatment room will run you about 10K extra. You also need a sophisticated HVAC system since your retail area needs to be 6-8 degrees warmer than your treatment rooms since no one is naked or in a robe while they shop.
3 treatment rooms, nail area, changing room, relaxation area, employee area, back office, retail space and reception would run about 2000 sq ft, and that is cutting it tight.
Retail space means you have to have products to sell. The most successful spas do about 50% of their revenue from product sales. So you have to bring in a couple of lines to offer, ideally one that you use in your skin and body treatments which helps sell the products. Even a middle of the road line like Pevonia or Dermalogica requires an opening order of $5 - 10K each.
You will also need computers, spa software, credit card processing, bags and boxes for your retail sales, menus, appt cards, advertising. 10K easy.
Don't forget your 1st months rent, security deposit and legal fees for reviewing / negotiating your lease. Another 5 - 10K depending on rent.
You will need at least a week of training for your retail and spa teams, all of which cost an hourly rate but generate no revenue. Another grand down the tubes.
Most importantly, you should have enough cash on hand to cover 3 months of operating expenses (rent, insurance, utilities, etc)
Don't count on your business making money for 6 months.
90% of business failures are due to capital shoreforum.xxxes, not due to some inherent flaw of the quality of or need for the business. Poor planning and poorer funding is what will do you in.