best kit to buy

I am looking to start brewing. I have done some extract 1g batches in my kitchen. But I want to start all grain and I want equipment that will last years even once I want to expand. I am leaning towards a gravity system and I want everything large enough to do 5 gallon full boil batches and high gravity 5 gallon full boils. I guess I am asking what do I need and what should I get

All depends how complex you want to get and how much money you want to spend. As a general rule plastic has a limited life. Stainless lasts a long time. I began all grain with a simple gravity system that used two igloo coolers converted to HLT and MLT and a keggle. That cost me about $500. You can do BIAB with a turkey fryer set up and be under $200. There are so many options and so many different vendors it's hard to say one is better than another. Everyone tweaks their system so expect to buy more later. If you are limited on funds I would say stick to extract, make a keggle for a full boil then go for a fermenting chamber so you can control your temperatures.

So two questions on that. I can use a keggle for a mlt and hlt as long as the correct things are added right? Then essentially have a 3 keggle system? Other question is isn't it basically impossible to do high gravity with biab method

Yes! You can convert keggles to HLT and MLT just like the igloo cooler. BIAB gravity is limited to the size of the bag you put the grain in. To get a higher gravity you just boil longer. With a refractometer you can check gravity during a boil to figure out when you hit the preboil gravity you want then start timer and hops additions as normal. You will get a little more carmelization with a longer boil but if the heat is kept down it won't be too bad. It all depends what kinds of beers you like to make.

I like things like hoptimum and hop stupid. And pliny the elder. I like lots of hops but with low malt character. And essentially is what I want to make. Any good recipes for said beers would be awesome