heartleaf philodendron

What are the Brown stems coming off it there is about 5 of them

They are aerial roots. You can read about them on the Wiki link below.

Here is a link that might be useful: Philodendron roots

What are the Brown stems coming off it there is about 5 of them

Can I cut them off

Well, yes, but they are growing for a purpose - to find something to support the plant as it grows. You'd be better to find something suitable for it to be attached to otherwise the weight of the leaves will eventually cause it to topple.
Doesn't have to be an "ugly stake" you might find a nice branch or a piece of driftwood, there are also purpose made plant poles for indoors types

Well since they have started to grow all my new leaf have started to turn yellow

Since I noticed them growing my new leads have been turning yellow

looks like an immature monstera to me.

I have had the plant for 7 months when I got it it was 3 in tall when/ how long till it would start to mature