Tim Soundproofing is great but IMO NOT a necessity. Certainly not the first thing one would buy or worry about. The basics for any recording system are
1. a decent mic (preferably a tube or condenser)
2. a DAW or computer (I would go with a pc)
3. recording software. (There are freebies like Audacity that will do the basic job)
4. Audio interface.
5. Good studio monitors.
6. Instruments (guitars and a midi keyboard)

Each part of the chain can be upgraded piece by piece and extras like soundproofing and software (plugins) can be added as needed and when affordable.
Of course learning to be a recording engineer is a long and steep learning curve so it is better to start simply. Once the basics have been mastered then you can progress to the next level and purchase more advanced pro equipment.

It is difficult to offer proper advice when you do not know the experience, skill levels, type of music and financial circumstances of the person asking.

Some people will spend more on a mic or a single piece of equipment than others spend in their whole recording outlay.

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