Ok. You have decided to go into mining now how to start?

The gold standard is to build a mining RIG. There are a lot of good tutorials online how to do this step by step.

One good example would be this one. But would I recommend this for everybody wanting to go into mining? Well it depends.

"All-in" on mining

You want to go into mining "all in" and you can afford investing 5k. Then go ahead. Do some research on RIG building. Follow advice one a tutorial that suits you and go ahead. 

But that does not be the way for everyone. The money you need to build a complete rig is pretty significant and it can always happen that mining become non-profitable for a while. Then you have a rig idling around and don't make money of it. If the crypto market reach a period where mining is not profitable my advice would be: Shut down the rig, take the money you would need for electricity costs of the rig and buy crypto of that money on a onthly base. I would not sell the rig as soon as it gets unprofitable unless you REALLY need the money. Profitability is pretty volatile on mining, so a period where mining gets profitable again might come back very soon. And as possible profit rises, also prices for GPUs rises a lot. What you can consider might be selling GPUs that might become unprofitbale soon. At beginning of 2021 would be cards with 3 or 4GB of memory. And then replacing them later with GPUs with 6 GB or more of memory.

RIG alternatives

Another point why you might not want not to build a rig might be simply pratical reasons. Maybe you have a small appartment and you don't want a huge machine, making lot of noise and not looking really inviting for your friends and family visting you. A pretty good option is also to buy pre-build computer and let them do the work. Even having couple of computer standing around if you flat or house won't spoil up beauty of your dwelling.

And as always I urge you to be creative. I know that if you want to limit space used they are options to minimise this. There are computers that can host more than 1 GPU. This is often used for grid computing or 3d rendering or modelling. So do some research of what computers are used for that. Also some gamers build their computers on a multi gpu setup. 

One example would be dell precision 5400 workstations. The have 2 16x epci slots and a decent power supply. You can find such workstations on ebay or small advertisments for little money. You can pimp them with new or used gpus and depending on the setup with a bit ram or a SSD. Having such a workstation standing around in the basement or lumber room won't hurt muchen even in an apartment. Also the financial invest is managable and can give a ready to invest back revenue.

starting small option

Even starting even smaller can be a profitable option. What kind of computer do you have at home? Does it have a decent GPU? It might be worth replacing your GPU by a recent model and selling of your old one. Take a look of which one are currently most profitable. Currently good GPUs have a return of invest in 5-8 months as long as you are not seeking out for the top tier card.