There are some questions that I can ask (but I doubt if you will answer it ).

Are you buying Bitcoin for the long-term or short-term?
Can you afford to lose that amount of money?
Are you a newbie with regards to investing into cryptocurrency?

This is only my opinion. If you're buying Bitcoin hoping to make profit for the short-term, there's still some profits that you can get, but I would say investing into altcoins would give you more profit than Bitcoin at its current price. Now if you're planning for long-term, I would suggest waiting for the bear market to happen so you can buy those Bitcoins at a much lower price. I know the excitement of investing into Bitcoin especially when you already have the money but be patient especially now that we are in a bull market already. In short, I would say avoid because I feel it's too late, but hey it's your own money and whatever you feel trust that feeling of yours.

If I'm in your situation though, I would stop accumulating Bitcoin for now and focus on altcoins.

I think you misinterpreted something from Op. Op meant he/she has will be able to invest $300-$400 monthly, i don't think this means he/she earns that figure monthly.

I think this is dependent on the Op investment plan, how long does he/she wants to HODL the coin before taking profit.

While the price of bitcoin seems like crazily high now, people current view of the market shows even after hitting $100k many will still be HODLing maybe probably to the 150k. This means Op can still invest now but that doesn't means he/she should just go all out because can go side ways at times and so it's important to invest, what will not make life difficult for you in order not to sell your coins in lost. Also, if your plans is actually a long term like 5 to 10 years, you won't have to worry much about the current price because there's an high tendency of it already passing $200k by then.