Of course it’s fine to make use of Catholic sacramentals and prayer practices - the more the merrier! But not the sacramENTS - non-Catholics can’t present themselves for Communion in our churches, for example.
‘Legitimate’ form of Christianity? Well, we don’t believe that all Protestants automatically go to Hell, or anything like that, if that’s what you mean. Although we DO believe that the sacraments of the Catholic (and Orthodox) churches offer unique and especially helpful means towards salvation, not that they guarantee it. And that Catholic teaching offers the fullest possible truth (and remember Christ promised to lead the Apostles, and through them His church, into ALL truth).
We do believe that Protestant sects, in as much as they possess many of the essential truths of salvation, aren’t illegitimate. Of course the more out-there belief-wise a sect is, eg Seventh Day Adventists or Mormons, the less legitimacy it possesses.
Anglicans tend to share most of the essential Christian truths, so would rate fairly high in the legitimacy stakes, the more ‘High Church’ your beliefs the better.
Proper form of reverence in a Catholic church? Firstly you might see a bowl or stoop containing holy water near the door as you enter - feel free to dip your hand in and make the sign of the cross with it, it’s a sacramental.
Then look around - you may see a box- or container-type (either metal or covered in fabric) object with a light burning near it (usually red) somewhere in the Church. Most often front and centre behind the altar or to one side of it.
This is called the Tabernacle, which contains the reserved Eucharistic bread. Since we believe in the Real Presence of Jesus in the Eucharist, which continues even after reception by the faithful of Communion, if you can see the Tabernacle it you should genuflect (down on one knee and then up again) in its direction.
If you can’t see it, just make a reverent bow towards the altar.
In terms of other behaviour, just observe the common courtesies. No loud talking, turn the cellphone off, try not to take pictures and stuff.
Don’t go into the sanctuary - the area directly around the altar, usually separated visibly from the rest of the Church by stairs or rail or something. It’s reserved only for the priest and those assisting him.
If a Mass is going on, take your cue from the people around you - stand when they stand, sit when they sit, kneel when they kneel. For this reason it’s best not to sit near the front.
Feel free to join in any of the prayers and hymns you want, if you know them (I’ve attended an Anglican Mass, fairly high-church, the prayers were very similar to Catholic Mass). But don’t interrupt the priest, so none of the Evangelical ‘Amen-ing’ and ‘Alleluia-ing’.
Be aware that the Lord’s Prayer for Catholics DOESN’T include the words ‘for thine is the kingdom, the power and the glory’ (the most obvious way to spot a non-Catholic is when they launch into this

), although they are included in the words of the Mass at a later point.