While the question is very localized, I'll answer about the general principle.
My main question is with how far away it is (over 1000 miles), how do
I quantify the travel expenses?
Generally, "necessary and ordinary" expenses are deductible. This is true for business and also true for rentals. But what is necessary and what is ordinary? Is it ordinary that a landlord will manage the property 1000 miles away by himself on a daily basis? Is it ordinary for people to drive 1000 miles every week? I'd say "no" to both. I'd say it would be cheaper for you to hire a local property manager, thus the travel expense would not be necessary. I would say it would be cheaper to fly (although I don't know if its true to the specific situation of the OP, but as I said - its too localized to deal with) rather than drive from Texas to Colorado.
If the OP thinks that driving a thousand miles is indeed ordinary and necessary he'll have to justify it to the IRS examiner, as I'm sure it will be examined.
2 trips to the property a year will be a nearly 100% write-off (2000
miles, hotels, etc).
From what I understood (and that is what I've been told by my CPA), IRS generally allows 1 (one) trip per year per property. If there's an exceptional situation - be prepared to justify it. Also, keep all the receipts (like gas, hotel, etc.... If you claim mileage but in reality you took a flight - you'll get hit hard by the IRS when audited).
Also while I'm up there am I allowed to mix business with pleasure?
You cannot deduct personal ("pleasure") expenses, at all. If the trip is mainly business, but you go out at the evening instead of staying at the hotel - that's fine. But if the trip is "business" trip where you spend a couple of hours at your property and then go around having fun for two days - the whole trip may be disallowed. If there's a reasonable portion dedicated to your business/rental, and the rest is pleasure - you'll have to split some of the costs and only deduct the portion attributed to the business activities.
You'll have to analyze your specific situation, and see where it falls. Don't stretch the limits too much, it will cost you more on the long run after all the audits and penalties.
Can I also write off all travel involved in the purchase of the
Although, again, the "necessary and ordinary" justification of such a trip is arguable, lets assume it is necessary and ordinary and generally justified. It is reasonable to expect you to go and see the property with your own eyes before the closing (IMHO, of course, I'm not an authority). Such an expense can be either business or investment expense. If its a business expense - its deductible on schedule C. If its an investment expense (if you do buy the property), its added to the cost of the property (capitalized).
I'm not a tax adviser or a tax professional, and this is not a tax advice. This answer was not written or intended to be used, and cannot be used, for the purpose of avoiding any tax related penalties that may be imposed on you or any other person under the Internal Revenue Code.
You should seek a professional consultation with a CPA/Attorney(tax) licensed in your State(s) or a Federally licensed Enrolled Agent (EA).