Your biggest overhead category is staff salaries and benefits. I can't emphasize enough how important it is to choose the right staff. Also, nip staff problems in the bud, document deficiencies and if those warnings are not heeded, replace people who are not working well for you. I have a very small staff that I pay well and treat well, and they know it.
Space is you second biggest expense. You need enough to get you off the ground but you shouldn't over-rent. Every square foot costs, and especially if you are building out, every square foot should add something of value. Plan on having two exam rooms within a year and if possible a third within the first five years. You need space for diagnostic devices--camera, perimeter and OCT.
Your own draw for personal expenses needs to be considered in your startup budget. Minimizing that figure is essential. Don't forget health insurance and other important expenses.
Utilities add up: you will need electric and possibly gas service. Phone service can be done different ways, including through your cable provider, you need internet. You will need to have your office cleaned, so budget a few hundred a month for that. You will need basic office supplies and an inventory of medical supplies. That will come to $3-4K in a startup. You will need some kind of copier, although if you start out with digital charts, then an all-in one laser with fax might be enough. You can always upgrade that stuff later. You might want a couple of trays of instruments for small procedures, maybe a couple of smaller trays for irrigations and foreign body removals, a steam sterilizer is key (I like Ritter, but there are other good ones, too.) instrument wrap, sterilizer pouches, steam indicator strips and tape, instrument cleaning supplies (little toothbrush, soap, distilled water, instrument milk).
An ultrasound cleaner is very useful for processing instruments.
An equipment budget should include what you need in lane equipment as well as the small but pricy items like a Hertel, etc., office furniture and appliances, computers, software and network installation along with some IT support.
Lasers are an individual decision. I have day-rented SLTs, and that was OK, and now I own a diode laser, and that is OK. I would have saved money doing the leasing, but I am less tied down to scheduling laser procedures now that I own the laser and can move it relatively easily between my offices. One of my surgery centers has a nice Ellex YAG, but when I came across an opportunity to buy a nice used current model YAG, I bought one. Has it paid for itself? No. But I like the convenience. I did not start out with a laser, though. Unless you have none available to you or there is some feature of your practice that requires you have one from the start, then I suggest waiting a little before buying a laser.