If you are a gold 1 and you are playing with mainly onyx players but some diamonds too, then the ranking system is going to take into account that your teammates are higher ranked than you and you’re likely to come up against opponents that you shouldn’t be facing. I’d reccomend at least obtaining Onyx 1 on your own before you start playing with teams like this otherwise you’ll always be playing out of your depth. With all due respect, gold 1 is a low rank and you’re likely to face diamonds in some cases so id recommend playing alone for a while first as your rank progress is likely to be slow with teammates much better than you rank-wise.
And no, after your five placement games you can achieve onyx rank. I’m unsure as to the maximum rank you can achieve through placements though. I have achieved Onyx 3 after 5 placement games but in more recent seasons the system has been harsher. My friend @ColdChris1879 has obtained Diamond after his five placement games but again, this was not in recent seasons so the new maximum rank you can obtain is likely to have changed.
As for what the ranking system takes into account, I am not a member of TC so I obviously won’t take every little detail into account but I know that your placement on the team affects your rank, along with the size of your squad (if you’re playing in a stack), the overall skill rating of your team, the skill rating of the enemy team,( this is because the system uses this to predict a prerequisite winner and will rank you up or down according to the score), the margin that you win by (7-0 in Escalation is far better than a 7-6 win) and I believe your KD matters too. I know that score is counted so in that sense, Caps do affect your ranking at the end. Bounties equipped do not affect your rank.
If you want to go up, earn Onyx solo or play KOTH on a second account and get Onyx, otherwise you’re just going to be out of your depth and struggle, and I can’t imagine that will be much fun for you.
Hope this helps.