I can attest to starting small and having success along with gaining an understanding of what a good maintenance regimen can do for a system. I started with a 20 gallon long and an HOB (hang on the back) filter. I kept my start up costs low and slowly upgraded equipment as I advanced in the hobby. Fast forward almost 2 years I have a thriving mixed reef with very little death (knock on wood)I would say start with a 29 g or 40g breeder when petco has a $ per gallon sale or if u want something larger look on cl or fb marketplace for a larger one locally.
Buy job filter that's 3 to 5x turnover (tankvolume)
Buy filterfloss chemipure blue and carbon to put in it along with extra cartridges
Buy 2 to 3 150w heater 20 to 55$
And maybe a back up
Buy 55g drums or garbage cans
Have two one for fresh rodi one for saltwater and have a few buckets
Buy 2 small wavemakers 15 to 300$ depending on brand sun suns from China are cheap or u can overspec if money isnt an issue
But rember we want this to be a profitable/ cost effective endavour
Buy a 2ft 4 bulb t5ho or 165w chinese phlizon viparspectra or will led off amazon for 89$
A smaller tank without hardware will test u and make u a stronger fish keeper as you will learn propper maitence regime and get in the rhythm without hardware rember you take care of the coral not the hardware a machine cant do the job of a human sometime or they can but lack in certain aspects
Next is to buy a rodi unit that is 5 stage
This is close to 160$ but will save money and errors in the long haul as long as u keep up on filters every couple of months
Make 2 vats water
Make sure water test 0 ppm
Add powerheads and heater to one
Mix salt into one
Buy refractometer instant ocean salt and kh cal mag test kits
Buy all for reef powder or esv bionic 2 part for first 2 part as they are cheap and pretty much dummy safe
Buy quickstart or biospira to cycle tank
Mix ur first vat of salt at 1.025
Set up tank 29 or 40g sumpless for first tank add heater
Add bacteria wait a week add ammonium then turn on hob filter
Then add light
Wait a couple of days add wavemaker
When nitrogen cycle is over test tank to ensure 0 ammonia
Then add fish
Wait until tan reaches stasis then add coral
Test dkh cal mag daily and nitrates phosphate weekly, icp test once a year or every 6 months if you have many systems
If you start with a small tank and don't keep up with maintenance....you will NOT succeed.
Doing your research and not making spontaneous livestock or equipment purchases will make your introduction to the hobby a lot easier. A good saying to live by with this hobby is "nothing good can happen overnight but a lot of bad can" Good results will come with time but a lack of patience or research will lead to bad things quickly.