I would make sure to check out the wiki here: https://horsefable.wiki/ - This will have a lot of in depth answers for you. 

1. For career horses it doesn't matter too much when you're started but there's some good information the Career Wiki Page regarding what pages a good career horse. Personality matters in career, some personalities will perform better then other. I suggest starting as many cheap horses as you can in the Model Horse career as that center comes free with your account. Make sure they are personality is fully revealed as a personality test is 600 bucks. 

2. There are two types of competitions. Halter Shows and Discipline shows. Halter shows are good for foals and for 3-5 star horses. They are based on BS so the better your horse is, the better they'll perform. Halter's aren't generally recommended for new players for regular horses because you CAN lose money. Discipline shows are good long term for horse points after you get into tier 2. You can make a good amount of money and horse points from it once your horses have some PS and you're not struggling for money. This page talks mroe about about halter shows and also the different paths your horse can take: https://horsefable.wiki/halter-arena/

3. You can only buy items from other players so you'll need to keep in eye out for them in Market Trades. The only way they populate ingame at the moment is through explore encounters. 

4. If you post your horse links I can take a look. 

5. There's no more quests atm, but more are being developed so you're free to play the game however you'd like!

Thank you for the info! Here are some of the horses I have bought and so far my favorite! I figured I can train them and use them for model horses until I get the hang of other things :)

https://horsefable.com/horse/1490127 : Grandpas Rolex

https://horsefable.com/horse/1563664 : Afternoon Treat X Lady Goose Foal

https://horsefable.com/horse/1586852 : Jolene

https://horsefable.com/horse/1567903 : Mining For Gold

https://horsefable.com/horse/1572207 : Patchwork Love

https://horsefable.com/horse/1587051 : Hot N Cold

I did buy a few upgrades, but I'm starting to wonder if that will be my downfall as I wasn't sure what I needed to start out. I am down to 35k lol, if you have any advice on what I do need please tell! 

https://horsefable.com/horse/1490127 : Grandpas Rolex - This horse has a good amount of PS. It looks like from the History tab it is doing quite well in Cutting shows and is making a good profit. Keep entering it in Cutting shows and keep an eye to make sure you're making money. If you start loosing money, switch it to Careers for awhile. 

https://horsefable.com/horse/1563664 : Afternoon Treat X Lady Goose Foal - This one is low PS and no show history so just send it off to careers. 

https://horsefable.com/horse/1586852 : Jolene - Send to careers. From the history tab you can see it only net made $5 in discipline shows but is making 22$ in career. Careers have no entry fees so it's all profit!

https://horsefable.com/horse/1567903 : Mining For Gold - This one has a decent amount of PS so you could try entering like 2 disc shows one day and see how much money it makes compared to how much it makes in discipline and then go for whatever one you're getting the most money for.

https://horsefable.com/horse/1572207 : Patchwork Love - Same thing with this one. 

https://horsefable.com/horse/1587051 : Hot N Cold - this one is low PS - id send straight off to careers. 

- For your remaining 35k, I would start saving it up or only using it to invest in cheap horses from the rescue or from other players. If you join our discord server, sometimes players give away horses for free too so that can get help you get a good career herd going to bring in income. When you start getting a comfortable amount of income, you can start by showing your horses in disciplines. This in the very long run will get you more horse points/levels and your income gain/lose will level off, especially the more your herd grows. 

Thank you for the feedback on my horses! I'll see what I can do to join the server! I appreciate your help!