yes, mirrorless seems to fit his requirements.
Correct. The EOS-M system you mentioned however only has one native macro lens and its very short in focal length, which kind of reduces its usefulness, though the builtin ringflash is a nice touch.
The Fuji X system also currently lacks a really good macro lens. Theres hopefully one coming now.
But he recommends to try to get the best lenses first than upgrading the body because the lenses make a better improvement rate comparing to the bodies.
Correct. But unfortunately Nikon "DX" (aka crop format aka APS-C aka 24x16mm sensor size aka "half-frame" even if people here complain thats a Ken Rockwell term but I think its very intuitive) doesnt have that much in respect to good lenses in the first place. Namely good wide angle and good prime lenses are sparse, and thanks to the crop factor using FX lenses often doesnt work well as a fix, either. Which is why everyone who actually gets enthusiast about photography tends to switch to "FX" (aka small format aka 36x24mm sensor size aka 35mm film aka full frame). Or to other systems.
He said D5300 is suitable for me because of the swivel screen will help with the macro shots so I don't have to bend down as much.
Yes, but only if you do macro with Lifeview, i.e. if you put the DSLR out of its SLR mode and use it like a compact or digital mirrorless - basically filming in the sensor and displaying the result on the monitor. Unfortuantely this also means that your camera will be using contrast autofocus - for which the lenses havent been designed, thus its really slow on all Nikon DSLRs.
Also help with the street/candid shots if I positioned the camera at my stomach area so people won't know that I took a picture.
Only if they are deaf or not hearing the shutter sound for a different reason, and also not looking into your direction. And again, using the monitor requires lifeview. Which means your camera will only focus very slowly, and very unreliably on moving subjects. This isnt a property of lifeview per se, but its a property of lifeview on a Nikon DSLR.
The discussion how to shoot street photography though is endless. In my experience even a super stealthy specialist like the Ricoh GR is always noticed - the GR really helps me with friends who are camera shy, though.
Another point he made was the GPS to help locate the locations when I do landscape and street.
Mostly it will simply drain your battery. Which is why Nikon skipped over GPS for the successor of the D5300, the D5500.
He said the D3300 is fine but only for people who just want to move from their P&S to a basic dslr and be done with it. He said it most likely a problem for people who want to grow and they will grow quickly with the D3300 and want to upgrade already. So he think overall the financially may not best to go from D3300 to D5xxx in a short time. This is why he recommends the D5300, so people can grow in it and there is a chance that D5500 might be good enough for most people as their final camera as well.
The D3x00 and D5x00 lines are basically exactly the same thing.
However, the D3x00 line only gets the cheapest of the cheapest ingredients. It is the "low end".
While the D5x00 gets a flipscreen and the "good" stuff, like a top performing sensor, and a better autofocus.
They are both entry level DSLRs though. For example, menu surfing is a quite regular part of using them, because they lack a sufficient number of external controls to avoid that. Advanced features are missing. Their viewfinder are basically useless to check if things are in focus. Etc.
If you want a camera to grow with and really want to get into photography, get a semipro camera - a used D7100 from
eBay or alike, or the predecessor D7000, or the even ealier D90, or the current D7200. These cameras might be even all you ever need, especially if the reduced amount of lens choices doesnt bother you. Or they can be great crop cameras for you later, good for areas which benefit from crop factor - like wildlife (extreme telephoto needed) or macro (the smaller sensor is basically free additional magnification).
Or even one of the older, professional full frame cameras, like the D3 or D700. Mind though getting full frame cameras also requires getting full frame lenses - and those tend to be much more expensive. Except if you're open to the used market, an manual focus. Then you can get all-metal, high quality glas from ages past, for nothing short dirt cheap. Manual focus lenses are a lot of fun, however they also make moving subjects a true challenge.